Unaudited Quarterly Financial Data (Condensed) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summarized unaudited quarterly financial data
Interest income	$ 145,281	$ 142,395	$ 132,385	$ 126,116	$ 125,310	$ 122,905	$ 117,715	$ 103,066	$ 546,177	$ 468,996	$ 375,022
Interest expense	8,833	10,947	12,089	10,904	9,436	9,160	9,161	7,774	42,773	35,531	29,864
Net interest income	136,448	131,448	120,296	115,212	115,874	113,745	108,554	95,292	503,404	433,465	345,158
Provision for loan losses	0	0	0	57	1,246	3,194	4,718	795	57	9,953	10,824
Net interest income after provision for loan losses	136,448	131,448	120,296	115,155	114,628	110,551	103,836	94,497	503,347	423,512	334,334
Non-interest income	28,417	43,049	30,834	28,474	28,494	32,416	31,828	26,086	130,774	118,824	112,239
Non-interest expense	95,252	110,675	86,170	82,830	81,876	82,829	81,795	73,627	374,927	320,127	265,571
Income before income taxes	69,613	63,822	64,960	60,799	61,246	60,138	53,869	46,956	259,194	222,209	181,002
Federal and state income tax expense	12,203	12,212	12,568	11,667	11,647	10,802	9,485	8,397	48,650	40,331	64,625
Net Income	$ 57,410	$ 51,610	$ 52,392	$ 49,132	$ 49,599	$ 49,336	$ 44,384	$ 38,559	$ 210,544	$ 181,878	$ 116,377
Basic earnings per share	$ 0.62	$ 0.57	$ 0.61	$ 0.58	$ 0.59	$ 0.58	$ 0.53	$ 0.48	$ 2.39	$ 2.18	$ 1.50
Diluted earnings per share	$ 0.62	$ 0.57	$ 0.61	$ 0.58	$ 0.59	$ 0.58	$ 0.52	$ 0.48	$ 2.38	$ 2.17	$ 1.50