Annual report pursuant to Section 13 and 15(d)

Summary of Unaudited Quarterly Financial Information - Summary (Details)

v3.8.0.1
Summary of Unaudited Quarterly Financial Information - Summary (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]                      
Total revenues $ 50,465 $ 33,375 $ 27,995 $ 29,267 $ 38,185 $ 21,619 $ 19,521 $ 29,648 $ 141,102 $ 108,973 $ 71,914
Total operating costs and expenses 22,113 16,882 14,980 19,051 18,831 16,153 15,552 14,552 73,026 65,088 44,585
Income tax (expense) benefit (37,674) (3,645) (2,242) (1,114) (10,354) (160) 3,881 (3,694) (44,675) (10,327) 192,115
Net Income (loss) $ (7,007) $ 8,426 $ 6,058 $ 5,079 $ (3,125) $ 1,051 $ (6,170) $ 6,608 $ 12,556 $ (1,636) $ 229,824
Basic per share amounts:                      
Net income (loss) - Basic (USD per share) $ (0.33) $ 0.40 $ 0.29 $ 0.24 $ 0.15 $ 0.05 $ (0.30) $ 0.32 $ 0.60 [1] $ (0.08) [1] $ 11.61 [1]
Diluted per share amounts:                      
Net income (loss) - Diluted (USD per share) $ (0.33) $ 0.36 $ 0.26 $ 0.22 $ 0.15 $ 0.05 $ (0.30) $ 0.30 $ 0.53 [1] $ (0.08) [1] $ 10.83 [1]
Weighted average shares—basic (shares) 21,109 21,071 21,013 20,938 20,898 20,887 20,832 20,708 21,032 20,831 19,790
Weighted average shares—diluted (shares) 21,109 23,551 23,216 23,019 20,898 22,997 20,832 22,284 23,481 20,831 21,228
[1] The sum of net income per share amounts may not equal the total due to rounding