Summary of Significant Accounting Policies - Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ 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
Accounting Policies [Abstract]
Net income	$ 20,990	$ (13,276)	$ (410)	$ (2,935)	$ (259)	$ (5,506)	$ 20,733	$ (6,925)	$ 4,369	$ 8,043	$ 21,158
Weighted average number of common share outstanding — basic									26,703,577	25,568,371	24,630,898
Effect of dilutive share-based awards (in shares)									719,256	506,364	483,159
Weighted average number of common shares outstanding — diluted									27,422,833	26,074,735	25,114,057
Earnings per share:
Basic (in dollars per share)	$ 0.78	$ (0.50)	$ (0.02)	$ (0.11)	$ (0.01)	$ (0.21)	$ 0.81	$ (0.28)	$ 0.16	$ 0.31	$ 0.86
Diluted (in dollars per share)	$ 0.76	$ (0.50)	$ (0.02)	$ (0.11)	$ (0.01)	$ (0.21)	$ 0.79	$ (0.28)	$ 0.16	$ 0.31	$ 0.84
Antidilutive securities excluded (in shares)									28,681	810,571	276,846