Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 235,205	$ 233,802	$ 231,788	$ 229,071	$ 242,151	$ 239,523	$ 224,967	$ 115,880	$ 929,866	$ 822,521	$ 442,846
Interest expense	15,371	14,587	14,322	13,952	14,136	13,807	12,708	8,042	58,232	48,693	37,881
Net interest income	219,834	219,215	217,466	215,119	228,015	225,716	212,259	107,838	871,634	773,828	404,965
Provision for loan and lease losses	4,545	8,153	11,254	12,637	5,241	14,333	14,696	5,971	36,589	40,241	10,716
Non-interest income	69,345	61,372	81,102	63,905	50,305	62,165	45,466	23,238	275,724	181,174	122,895
Non-interest expense	185,911	183,194	201,918	192,619	190,856	182,558	214,131	96,518	763,642	684,063	364,661
Income before income taxes	98,723	89,240	85,396	73,768	82,223	90,990	28,898	28,587	347,127	230,698	152,483
Provision for income taxes	35,704	31,633	30,612	26,639	29,641	32,107	11,356	9,936	124,588	83,040	54,192
Net income	63,019	57,607	54,784	47,129	52,582	58,883	17,542	18,651	222,539	147,658	98,291
Dividends and undistributed earnings allocated to participating securities	96	84	93	84	146	142	83	113	357	484	788
Net earnings available to common shareholders	$ 62,923	$ 57,523	$ 54,691	$ 47,045	$ 52,436	$ 58,741	$ 17,459	$ 18,538	$ 222,182	$ 147,174	$ 97,503
Basic earnings per common share (usd per share)	$ 0.29	$ 0.26	$ 0.25	$ 0.21	$ 0.24	$ 0.27	$ 0.09	$ 0.17	$ 1.01	$ 0.79	$ 0.87
Diluted earnings per common share (usd per share)	0.28	0.26	0.25	0.21	0.24	0.27	0.09	0.16	$ 1.01	$ 0.78	$ 0.87
Cash dividends declared per common share	$ 0.16	$ 0.16	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15