Condensed Financial Information (parent company only) - Statement of Income and Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income
Gain on the sale of insurance subsidiary									$ 8,265
Gain on cancellation of subordinated debentures									1,250
Other income									4,441	$ 6,438	$ 5,404
Expenses
Interest expense	$ 6,440	$ 6,215	$ 6,171	$ 5,968	$ 5,893	$ 5,424	$ 5,408	$ 5,117	24,794	21,842	16,569
Salaries and employee benefits									101,908	96,499	85,413
Other expenses									15,669	14,239	11,142
INCOME BEFORE INCOME TAX	18,595	23,624	26,824	22,006	20,898	22,102	21,048	18,237	91,049	82,285	60,414
Income tax benefit (expense)	(4,418)	(6,557)	(8,856)	(5,834)	(5,638)	(5,980)	(5,888)	(4,617)	(25,665)	(22,123)	(15,884)
NET INCOME	14,177	17,067	17,968	16,172	15,260	16,122	15,160	13,620	$ 65,384	$ 60,162	44,530
Preferred stock dividends and discount accretion											(2,380)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									$ 65,384	$ 60,162	42,150
Net income	$ 14,177	$ 17,067	$ 17,968	$ 16,172	$ 15,260	$ 16,122	$ 15,160	$ 13,620	65,384	60,162	44,530
Other comprehensive income (loss)									268	4,780	(911)
Comprehensive income									65,652	64,942	43,619
Parent
Income
Dividends from subsidiaries									39,032	$ 53,231	$ 63,732
Gain on the sale of insurance subsidiary									8,265
Gain on cancellation of subordinated debentures									1,250
Other income									197	$ 538	$ 45
Total income									48,744	53,769	63,777
Expenses
Interest expense									6,661	6,616	3,531
Salaries and employee benefits									3,023	3,128	3,284
Net occupancy and equipment expenses									464	442	258
Other outside services									1,455	458	1,141
Professional services									636	409	648
Other expenses									1,234	1,132	870
Total expenses									13,473	12,185	9,732
INCOME BEFORE INCOME TAX									35,271	41,584	54,045
Income tax benefit (expense)									(974)	3,999	3,153
Income before equity in undistributed income of subsidiaries									34,297	45,583	57,198
Equity in undistributed (distributions in excess of) income of subsidiaries									31,087	14,579	(12,668)
NET INCOME									$ 65,384	$ 60,162	44,530
Preferred stock dividends and discount accretion											(2,380)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS									$ 65,384	$ 60,162	42,150
Net income									65,384	60,162	44,530
Other comprehensive income (loss)									268	4,780	(911)
Comprehensive income									$ 65,652	$ 64,942	$ 43,619