Net Income 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
Net Income per Share [Abstract]
Net income	$ 21,357	$ 3,916	$ 389	$ 7,414	$ (3,827)	$ 4,322	$ 5,853	$ 6,162	$ 33,076	[1]	$ 12,510	[1]	$ 20,132	[1]
Less: earnings allocated to RSUs									(1,028)		(305)		(450)
Net income (loss) available to common shareholders									$ 32,048		$ 12,205		$ 19,682
Weighted average number of common shares outstanding									29,661		29,260		29,031
Basic and diluted									$ 1.08		$ 0.42		$ 0.68

[1] There is no material difference between net income and comprehensive income.