Basic and Diluted Net Income Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Basic and Diluted Net Income Per Common Share
Net income available to common shareholders	$ 9,814	$ 7,738
Weighted Average Shares Outstanding
Basic (in shares)	53,620,349	56,512,227
Effect of Dilutive Securities (in shares)	579,861	612,232
Diluted (in shares)	54,200,210	57,124,459
Net income per common share Basic and Diluted (in dollars per share)	$ 0.18	$ 0.14
Antidilutive options excluded from calculation of net income per common share (in shares)	381,396	124,672