Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income (loss)	$ (3,732)	$ 19,375	$ 6,422	$ 68,235
Weighted average shares used to compute net income (loss) per share
Basic	19,707,036	19,294,022	19,597,181	18,993,068
Effective of dilutive options and restricted stock units		1,129,000	442,000	1,141,000
Diluted	19,707,036	20,422,609	20,038,657	20,133,644
Net income (loss) per share
Basic	$ (0.19)	$ 1.00	$ 0.33	$ 3.59
Diluted	$ (0.19)	$ 0.95	$ 0.32	$ 3.39