Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income	$ 8,034	$ 29,071	$ 10,154	$ 48,860
Weighted average shares used to compute net income per share
Basic	19,590,164	19,081,034	19,541,478	18,840,656
Effective of dilutive options and restricted stock units	490,000	1,286,000	471,000	1,115,000
Diluted	20,079,702	20,367,127	20,012,344	19,956,097
Net income per share
Basic	$ 0.41	$ 1.52	$ 0.52	$ 2.59
Diluted	$ 0.40	$ 1.43	$ 0.51	$ 2.45