Basic and Diluted Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic and Diluted Net Income Per Common Share
Net income available to common shareholders	$ 12,106	$ 12,224	$ 35,747	$ 37,236
Weighted Average Shares Outstanding
Basic (in shares)	51,890,984	52,856,846	52,216,540	53,132,952
Effect of Dilutive Securities (in shares)	743,341	902,460	828,836	906,105
Diluted (in shares)	52,634,325	53,759,306	53,045,376	54,039,057
Net income per common share
Basic (in dollars per share)	$ 0.23	$ 0.23	$ 0.68	$ 0.70
Diluted (in dollars per share)	$ 0.23	$ 0.23	$ 0.67	$ 0.69
Stock based compensation awards that were excluded from the dilutive calculations as the effect would have been antidilutive (in shares)	1,130,653	341,174	839,628	341,174