Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 50,244	$ 64,080	$ 53,533
Denominator:
Denominator for basic earnings per share - weighted average shares (in shares)	31,419	30,276	28,435
Effect of dilutive employee stock options and restricted stock (in shares)	884	809	508
Denominator for diluted earnings per share - adjusted weighted average shares and assumed exercised (in shares)	32,303	31,086	28,943
Earnings per share:
Basic (in dollars per share)	$ 1.60	$ 2.12	$ 1.88
Diluted (in dollars per share)	$ 1.56	$ 2.06	$ 1.85
Outstanding common stock equivalents having no dilutive effect	2	18	83