Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basic earnings per common share:
Net income available to common shareholders	$ 24,872	$ 17,946	$ 48,798	$ 33,790
Weighted-average basic common shares	23,981	23,892	23,947	23,882
Basic earnings per common share (in dollars per share)	$ 1.04	$ 0.75	$ 2.04	$ 1.41
Diluted earnings per share:
Net income available to common shareholders	$ 24,872	$ 17,946	$ 48,798	$ 33,790
Weighted-average basic common shares	23,981	23,892	23,947	23,882
Effect of dilutive securities (in shares)	277	249	267	244
Weighted-average dilutive shares	24,258	24,141	24,214	24,126
Diluted earnings per common share (in dollars per share)	$ 1.03	$ 0.74	$ 2.02	$ 1.40