Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ 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
Net income applicable to common stock	$ 23,635	$ 23,179	$ 22,900	$ 21,216	$ 21,160	$ 16,220	$ 15,394	$ 15,240	$ 90,930	$ 68,014	$ 59,582
Average common shares outstanding (shares)									41,737,636	35,971,877	31,499,498
Net income per common share - basic (usd per share)	$ 0.56	$ 0.55	$ 0.54	$ 0.53	$ 0.53	$ 0.40	$ 0.49	$ 0.48	$ 2.18	$ 1.89	$ 1.89
Diluted
Net income applicable to common stock	$ 23,635	$ 23,179	$ 22,900	$ 21,216	$ 21,160	$ 16,220	$ 15,394	$ 15,240	$ 90,930	$ 68,014	$ 59,582
Average common shares outstanding (shares)									41,737,636	35,971,877	31,499,498
Effect of dilutive stock-based compensation (shares)									251,819	255,562	260,149
Average common shares outstanding - diluted (shares)									41,989,455	36,227,439	31,759,647
Net income per common share - diluted (usd per share)	$ 0.55	$ 0.55	$ 0.54	$ 0.52	$ 0.52	$ 0.40	$ 0.48	$ 0.48	$ 2.17	$ 1.88	$ 1.88