Summary of Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Interest income	$ 357,395	$ 343,942	$ 329,834	$ 313,134	$ 306,934	$ 297,652	$ 285,510	$ 272,401	$ 1,344,305	$ 1,162,497	$ 1,022,803
Net interest income	297,933	291,619	284,577	274,284	269,713	262,572	251,097	239,927	1,148,413	1,023,309	899,180
Provision for loan losses	12,149	14,982	11,790	12,776	8,565	39,686	10,260	8,674	51,697	67,185	28,000
Income before income taxes	143,854	128,008	142,117	133,375	103,966	152,675	117,791	105,704
Income tax expense	38,784	18,949	30,936	30,209	74,361	54,668	41,788	33,847	118,878	204,664	141,667
Net income	105,070	109,059	111,181	103,166	29,605	98,007	76,003	71,857	428,476	275,474	246,784
Net income available common shareholders	$ 101,919	$ 99,330	$ 108,622	$ 100,607	$ 27,046	$ 95,448	$ 73,444	$ 69,298	$ 410,478	$ 265,236	$ 236,546
Net income per common share, basic (in dollars per share)	$ 0.88	$ 0.85	$ 0.92	$ 0.85	$ 0.23	$ 0.79	$ 0.60	$ 0.57	$ 3.49	$ 2.19	$ 1.90
Net income per common share, diluted (in dollars per share)	$ 0.87	$ 0.84	$ 0.91	$ 0.84	$ 0.23	$ 0.78	$ 0.60	$ 0.56	$ 3.47	$ 2.17	$ 1.89