Unaudited Quarterly Financial Data (Condensed) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summarized unaudited quarterly financial data
Interest income	$ 171,308	$ 157,487	$ 155,404	$ 142,865	$ 145,281	$ 142,395	$ 132,385	$ 126,116	$ 627,064	$ 546,177	$ 468,996
Interest expense	5,550	6,084	7,185	8,496	8,833	10,947	12,089	10,904	27,315	42,773	35,531
Net Interest Income	165,758	151,403	148,219	134,369	136,448	131,448	120,296	115,212	599,749	503,404	433,465
Provision for credit losses	(1,535)	5,186	16,929	19,185	0	0	0	57	39,765	57	9,953
Net interest income after provision for credit losses	167,293	146,217	131,290	115,184	136,448	131,448	120,296	115,155	559,984	503,347	423,512
Non-interest income	44,704	53,667	41,224	33,272	28,417	43,049	30,834	28,474	172,867	130,774	118,824
Non-interest expense	111,187	103,373	94,764	95,487	95,252	110,675	86,170	82,830	404,811	374,927	320,127
Income Before Income Taxes	100,810	96,511	77,750	52,969	69,613	63,822	64,960	60,799	328,040	259,194	222,209
Federal and state income tax expense	18,950	18,754	14,306	9,630	12,203	12,212	12,568	11,667	61,640	48,650	40,331
Net Income	$ 81,860	$ 77,757	$ 63,444	$ 43,339	$ 57,410	$ 51,610	$ 52,392	$ 49,132	$ 266,400	$ 210,544	$ 181,878
Basic earnings per share (in dollars per share)	$ 0.86	$ 0.81	$ 0.67	$ 0.46	$ 0.62	$ 0.57	$ 0.61	$ 0.58	$ 2.81	$ 2.39	$ 2.18
Diluted earnings per share (in dollars per share)	$ 0.86	$ 0.81	$ 0.66	$ 0.46	$ 0.62	$ 0.57	$ 0.61	$ 0.58	$ 2.81	$ 2.38	$ 2.17