Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic earnings per common share:
Net income available to common shareholders	$ 25,140	$ 19,327	$ 73,938	$ 53,116
Weighted-average basic common shares	23,984	23,899	23,956	23,890
Basic earnings per common share (in dollars per share)	$ 1.05	$ 0.81	$ 3.09	$ 2.22
Diluted earnings per share:
Net income available to common shareholders	$ 25,140	$ 19,327	$ 73,938	$ 53,116
Weighted-average basic common shares	23,984	23,899	23,956	23,890
Effect of dilutive securities (in shares)	301	261	279	249
Weighted-average dilutive shares	24,285	24,160	24,235	24,139
Diluted earnings per common share (in dollars per share)	$ 1.04	$ 0.80	$ 3.05	$ 2.20