Basic and Diluted Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Basic and Diluted Net Income Per Common Share
Net income available to common stockholders	$ (5,942)	$ 6,385	$ 7,896	$ 5,458	$ 7,716	$ 12,106	$ 12,580	$ 11,061	$ 13,797	$ 43,463	$ 49,370
Weighted Average Shares Outstanding
Basic (in shares)	50,255	50,246	50,225	50,308	50,970	51,891	52,314	52,451	50,259	51,902	53,042
Effect of dilutive securities (in shares)									764	807	899
Diluted (in shares)	51,081	50,984	50,987	51,041	51,710	52,634	53,179	53,330	51,023	52,709	53,941
Basic net income per common share (in dollars per share)	$ (0.12)	$ 0.13	$ 0.16	$ 0.11	$ 0.15	$ 0.23	$ 0.24	$ 0.21	$ 0.27	$ 0.84	$ 0.93
Diluted net income per common share (in dollars per share)	$ (0.12)	$ 0.13	$ 0.15	$ 0.11	$ 0.15	$ 0.23	$ 0.24	$ 0.21	$ 0.27	$ 0.82	$ 0.92
Stock based compensation awards excluded from the dilutive calculations as the effect would have been antidilutive (in shares)									1,200	800	300