Summary of Significant Accounting Policies - Earnings Per Share (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
Summary of Significant Accounting Policies
Weighted average shares, issuance of restricted stock									100	100	100
Nonvested restricted stock shares excluded from total weighted average shares	0				100				0	100	300
Numerator:
Basic net income (loss)	$ (23,545)	$ (1,477)	$ 647	$ 2,439	$ 17,058	$ 11,897	$ 117,361	$ 791	$ (21,936)	$ 147,107	$ 11,950
Effect of diluted securities										2,969
Diluted net income (loss)									$ (21,936)	$ 150,076	$ 11,950
Denominator:
Basic weighted average shares outstanding (in shares)									22,493	22,346	22,010
Effect of diluted securities (in shares)										4,163	120
Diluted weighted average shares outstanding (in shares)									22,493	26,509	22,130
Basic earnings (loss) per share (in dollars per share)	$ (1.05)	$ (0.07)	$ 0.03	$ 0.11	$ 0.77	$ 0.53	$ 5.24	$ 0.04	$ (0.98)	$ 6.58	$ 0.54
Diluted earnings (loss) per share (in dollars per share)	$ (1.05)	$ (0.07)	$ 0.03	$ 0.11	$ 0.68	$ 0.49	$ 4.45	$ 0.04	$ (0.98)	$ 5.66	$ 0.54