Quarterly Financial Information (Unaudited) (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | 12 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2015 |
Dec. 31, 2014 |
Sep. 30, 2014 |
Jun. 30, 2014 |
Mar. 31, 2014 |
Dec. 31, 2013 |
Sep. 30, 2013 |
Jun. 30, 2013 |
Mar. 31, 2013 |
Jun. 30, 2015 |
Jun. 30, 2014 |
Dec. 31, 2014 |
Dec. 31, 2013 |
Dec. 31, 2012 |
|
| Quarterly Financial Information | ||||||||||||||
| Total operating revenues | $ 100,718 | $ 71,583 | $ 57,441 | $ 36,532 | $ 22,942 | $ 16,994 | $ 11,980 | $ 6,318 | ||||||
| Total operating expenses | $ 51,333 | 42,758 | 34,840 | 33,653 | 20,965 | 37,797 | 7,864 | 6,216 | 4,178 | $ 103,255 | $ 54,618 | $ 132,216 | $ 56,055 | $ 5,354 |
| Operating income (loss) | $ 36,760 | 57,960 | 36,743 | 23,788 | 15,567 | (14,855) | 9,130 | 5,764 | 2,140 | $ 70,673 | $ 39,355 | 134,058 | 2,179 | (4,707) |
| Net income (loss) | $ 55,898 | $ 34,288 | $ 22,380 | $ 15,309 | $ (14,904) | $ 9,078 | $ 5,720 | $ 2,121 | $ 127,875 | $ 2,015 | $ (4,715) | |||