Condensed Financial Information (parent company only) - Statements of Income and Comprehensive Income (Details) - USD ($) $ 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
Income
Other income									$ 2,068	$ 2,699	$ 992
Expenses
Interest expense	$ 28,237	$ 29,200	$ 27,361	$ 23,947	$ 20,769	$ 18,314	$ 16,300	$ 13,704	108,745	69,087	37,612
Salaries and employee benefits									144,037	131,704	119,812
Other expenses									17,804	16,966	15,543
Income before income tax expense	56,128	43,094	48,805	45,758	47,662	49,591	47,595	43,290
Income tax benefit	(8,298)	(6,337)	(7,749)	(6,941)	(5,949)	(8,478)	(7,961)	(6,611)	(29,325)	(28,999)	(37,524)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									164,460	159,139	96,070
Net income	$ 47,830	$ 36,757	$ 41,056	$ 38,817	$ 41,713	$ 41,113	$ 39,634	$ 36,679	164,460	159,139	96,070
Other comprehensive income (loss)									49,296	(17,888)	10,673
Comprehensive income									213,756	141,251	106,743
Parent
Income
Dividends from subsidiaries									125,775	100,954	33,014
Loss on sale of available for sale securities									0	0	(50)
Other income									172	572	350
Total income									125,947	101,526	33,314
Expenses
Interest expense									8,309	8,233	7,572
Salaries and employee benefits									3,540	3,729	4,118
Net occupancy and equipment expenses									802	851	797
Other outside services									1,889	489	1,810
Professional services									303	270	442
Other expenses									1,587	442	(385)
Total expenses									16,430	14,014	14,354
Income before income tax expense									109,517	87,512	18,960
Income tax benefit									3,575	3,298	5,946
Income before equity in undistributed income of subsidiaries									113,092	90,810	24,906
Equity in undistributed income of subsidiaries									51,368	68,329	71,164
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									164,460	159,139	96,070
Net income									164,460	159,139	96,070
Other comprehensive income (loss)									49,296	(17,888)	10,673
Comprehensive income									$ 213,756	$ 141,251	$ 106,743