Condensed Financial Information (parent company only) - Statement of Income and Comprehensive Income (Details) - USD ($) $ 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
Income
Other income									$ 5,192	$ 2,970	$ 3,594
Expenses
Interest expense	$ 20,769	$ 18,314	$ 16,300	$ 13,704	$ 11,583	$ 10,427	$ 8,367	$ 7,235	69,087	37,612	26,839
Salaries and employee benefits									131,704	119,812	102,552
Other expenses									16,966	15,543	15,470
INCOME BEFORE INCOME TAX	47,662	49,591	47,595	43,290	39,593	32,297	31,343	30,361
Income tax benefit	(5,949)	(8,478)	(7,961)	(6,611)	(15,210)	(7,939)	(7,207)	(7,168)	(28,999)	(37,524)	(27,609)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									159,139	96,070	81,051
Net income	$ 41,713	$ 41,113	$ 39,634	$ 36,679	$ 24,383	$ 24,358	$ 24,136	$ 23,193	159,139	96,070	81,051
Other comprehensive income (loss)									(17,888)	10,673	(12,219)
Comprehensive income									141,251	106,743	68,832
Parent
Income
Dividends from subsidiaries									100,954	33,014	33,546
Loss on sale of available for sale securities										(50)
Other income									572	350	143
Total income									101,526	33,314	33,689
Expenses
Interest expense									8,233	7,572	7,185
Salaries and employee benefits									3,729	4,118	639
Net occupancy and equipment expenses									851	797	832
Other outside services									489	1,810	967
Professional services									270	442	279
Other expenses									442	(385)	(470)
Total expenses									14,014	14,354	9,432
INCOME BEFORE INCOME TAX									87,512	18,960	24,257
Income tax benefit									3,298	5,946	3,243
Income before equity in undistributed income of subsidiaries									90,810	24,906	27,500
Equity in undistributed income of subsidiaries									68,329	71,164	53,551
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									159,139	96,070	81,051
Net income									159,139	96,070	81,051
Other comprehensive income (loss)									(17,888)	10,673	(12,219)
Comprehensive income									$ 141,251	$ 106,743	$ 68,832