Net Income per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 14,018	$ 9,713	$ 49,646	$ 42,406
Less distributed and undistributed earnings allocated to participating securities	248	229	909	962
Net Income (Loss) Available to Common Stockholders, Basic	$ 13,770	$ 9,484	$ 48,737	$ 41,444
Weighted average common shares outstanding basic (in shares)	20,629	20,869	20,597	20,972
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	109	15	105	10
Weighted Average Number of Shares Outstanding, Diluted	20,738	20,884	20,702	20,982