| In millions, except per share items | Sep-30-14 | Jun-30-14 | Mar-31-14 | Dec-31-13 | Sep-30-13 | Jun-30-13 | Mar-31-13 | Dec-31-12 |
| | 10-Q | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K |
| Cash flows from operating activities: | | | | | | | | |
| Net income | -42.5 | -45.7 | 75.0 | | 81.2 | 2.6 | 69.6 | |
| Adjustments to reconcile net income to net cash from operating activities: | | | | | | | | |
| Depreciation, depletion and amortization | 183.6 | 175.9 | 172.8 | | 173.8 | 114.6 | 106.8 | |
| Accretion of asset retirement obligations | 13.0 | 11.9 | 11.0 | | 10.6 | 6.6 | 5.8 | |
| Recognition of unit-based awards | 11.0 | 10.3 | 10.0 | | 9.3 | 5.6 | 3.2 | |
| Loss (gain) on derivative contracts, net | 135.1 | 129.3 | 3.9 | | -46.5 | -26.0 | -68.6 | -52.0 |
| Cash received (paid) on settlement of derivative contracts | -2.0 | 9.9 | 27.2 | | 35.7 | 37.5 | | |
| Other items | 12.0 | 9.3 | 8.1 | | 7.8 | 6.1 | 5.5 | |
| Changes in operating assets and liabilities: | | | | | | | | |
| Accounts receivable and other assets | -62.9 | -67.5 | -56.9 | -71.6 | -58.4 | -45.3 | -34.8 | -15.7 |
| Accounts payable and other liabilities | -23.4 | -9.1 | -0.9 | | 4.0 | 5.4 | 3.2 | |
| Net cash provided by operating activities | 255.8 | 263.1 | 277.2 | | 269.0 | 285.1 | | |
| |
| Cash flows from investing activities: | | | | | | | | |
| Additions to oil and natural gas properties | -310.7 | -257.1 | -223.0 | -211.7 | -250.8 | | | |
| Acquisitions | -241.9 | -299.4 | -261.2 | -229.9 | -569.6 | -693.1 | | |
| Proceeds from sale of available-for-sale securities | 5.3 | 6.2 | 5.3 | | 4.6 | | | |
| Purchases of available-for-sale securities | -10.0 | -10.7 | -10.4 | -10.2 | -4.3 | | | |
| Net cash used in investing activities | -552.4 | -557.0 | -485.1 | -442.9 | -817.0 | -972.7 | | |
| |
| Cash flows from financing activities: | | | | | | | | |
| Management incentive fee to the general partner | -7.6 | -8.2 | -7.5 | | | | | |
| Distributions to unitholders | -354.6 | -354.2 | -354.0 | -350.8 | -305.7 | -225.1 | -199.7 | -188.0 |
| Units withheld for employee payroll tax obligation | -2.2 | | | | | | | |
| Proceeds from bank borrowings | 364.0 | 336.0 | 228.0 | | 165.0 | 35.0 | | |
| Repayments on bank borrowings | -96.0 | -78.0 | | -60.0 | -531.5 | -803.0 | | |
| Deferred financing costs | | | | -7.5 | -14.4 | -17.9 | -19.7 | -17.8 |
| Other | | | | | -1.3 | -0.9 | | |
| Net cash (used in) provided by financing activities | 84.2 | 72.8 | -18.4 | | -78.5 | -98.1 | | |
| |
| Increase (decrease) in cash | -12.7 | -21.3 | -26.5 | -52.7 | -34.2 | -25.8 | -8.5 | |
| Cash and cash equivalents at beginning of period | 40.1 | 58.6 | 77.0 | | 95.5 | 63.7 | 49.3 | |
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| Cash and cash equivalents at ending of period | | | | | | | | |