Condensed Financial Information (parent company only) - Statements of Income and Comprehensive Income (Details) - USD ($) $ 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
Income
Other income									$ 1,898	$ 2,068	$ 2,699
Expenses
Interest expense	$ 10,913	$ 13,304	$ 16,234	$ 25,930	$ 28,237	$ 29,200	$ 27,361	$ 23,947	66,381	108,745	69,087
Salaries and employee benefits									155,937	144,037	131,704
Other expenses									18,001	17,804	16,966
Income before income tax expense	52,776	41,831	37,615	37,753	56,128	43,094	48,805	45,758
Income tax benefit	(7,641)	(5,621)	(4,623)	(3,490)	(8,298)	(6,337)	(7,749)	(6,941)	(21,375)	(29,325)	(28,999)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									148,600	164,460	159,139
Net income	$ 45,135	$ 36,210	$ 32,992	$ 34,263	$ 47,830	$ 36,757	$ 41,056	$ 38,817	148,600	164,460	159,139
Other comprehensive income (loss)									46,962	49,296	(17,888)
Comprehensive income									195,562	213,756	141,251
Parent
Income
Dividends from subsidiaries									70,100	125,775	100,954
Other income									(62)	172	572
Total income									70,038	125,947	101,526
Expenses
Interest expense									6,777	8,309	8,233
Salaries and employee benefits									3,426	3,540	3,729
Net occupancy and equipment expenses									745	802	851
Other outside services									731	1,889	489
Professional services									218	303	270
Other expenses									1,266	1,587	442
Total expenses									13,163	16,430	14,014
Income before income tax expense									56,875	109,517	87,512
Income tax benefit									2,260	3,575	3,298
Income before equity in undistributed income of subsidiaries									59,135	113,092	90,810
Equity in undistributed income of subsidiaries									89,465	51,368	68,329
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									148,600	164,460	159,139
Net income									148,600	164,460	159,139
Other comprehensive income (loss)									46,962	49,296	(17,888)
Comprehensive income									$ 195,562	$ 213,756	$ 141,251