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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 27,003	$ 24,808	$ 24,987	$ 43,484	$ 59,590	$ 45,663	$ 90,043	$ 56,157	$ 120,282	$ 251,453	$ 141,102
Total operating costs and expenses	37,182	29,966	29,117	29,738	26,441	22,301	19,868	19,116	126,003	87,726	73,026
Income tax (expense) benefit	810	4,620	3,609	(176,376)	14,307	(11,864)	(22,419)	(10,033)	(167,337)	(30,009)	(44,675)
Net income (loss)	$ (7,365)	$ (15,251)	$ (14,419)	$ 666,337	$ (42,482)	$ 67,362	$ 73,160	$ 45,279	$ 629,302	$ 143,321	$ 12,556
Basic per share amounts:
Net income (loss) - Basic (USD per share)	$ (0.43)	$ (0.81)	$ (0.74)	$ 32.59	$ (2.02)	$ 3.19	$ 3.45	$ 2.13	$ 33.13	$ 6.77	$ 0.60
Diluted per share amounts:
Net income (loss) - Diluted (USD per share)	$ (0.43)	$ (0.81)	$ (0.74)	$ 31.32	$ (2.02)	$ 2.80	$ 2.99	$ 1.83	$ 31.85	$ 5.96	$ 0.53
Weighted average shares—basic (shares)	17,243	18,770	19,558	20,447	21,071	21,148	21,212	21,209	18,995	21,160	21,032
Weighted average shares—diluted (shares)	17,243	18,770	19,558	21,277	21,071	24,052	24,438	24,800	19,757	24,067	23,481