Parent Company Financial Statements, Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Expenses:
Interest expense	$ 11,773	$ 11,797	$ 13,440
Other expenses	14,208	14,401	19,909
Income before income taxes and equity in undistributed income of subsidiaries	64,963	62,397	65,172
Income tax benefit	18,531	19,146	20,000
Net income	46,432	43,251	45,172
Unrealized holding gains (losses) on securities available-for-sale
Unrealized holding gains (losses) arising during the period	(342)	13,928	(31,878)
Less: Reclassification adjustments for realized losses included in net income	(106)	(211)	(45)
Other comprehensive income (loss), net of tax	(153)	9,190	(20,691)
Comprehensive income	46,279	52,441	24,481
Parent Company [Member]
Income:
Dividends from subsidiary banks	19,808	19,534	13,035
Other income	414	196	545
Total income	20,222	19,730	13,580
Expenses:
Interest expense	1,170	1,131	1,161
Depreciation expense	130	153	163
Other expenses	2,465	2,550	2,442
Total expenses	3,765	3,834	3,766
Income before income taxes and equity in undistributed income of subsidiaries	16,457	15,896	9,814
Income tax benefit	(1,371)	(1,548)	(1,416)
Income before equity in undistributed income of subsidiaries	17,828	17,444	11,230
Equity in undistributed income of subsidiaries	28,604	25,807	33,942
Net income	46,432	43,251	45,172
Unrealized holding gains (losses) on securities available-for-sale
Unrealized holding gains (losses) arising during the period	(342)	13,928	(31,878)
Less: Reclassification adjustments for realized losses included in net income	(106)	(211)	(45)
Tax expense (benefit)	(83)	4,949	(11,142)
Other comprehensive income (loss), net of tax	(153)	9,190	(20,691)
Comprehensive income	$ 46,279	$ 52,441	$ 24,481