Parent Company Financial Statements, Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Expenses [Abstract]
Interest expense	$ 13,555	$ 11,773	$ 11,797
Other expenses	12,077	11,780	11,980
Income before income taxes and equity in undistributed income of subsidiaries	66,464	64,963	62,397
Income tax benefit	19,118	18,531	19,146
Net income	47,346	46,432	43,251
Unrealized holding gains (losses) on securities available-for-sale [Abstract]
Unrealized holding gains (losses) arising during the period	(4,578)	(342)	13,928
Less: Reclassification adjustments for realized gains (losses) included in net income	522	(106)	(211)
Other comprehensive income (loss), net of tax	(3,315)	(153)	9,190
Comprehensive income	44,031	46,279	52,441
Parent Company [Member]
Income [Abstract]
Dividends from subsidiary banks	20,708	19,808	19,534
Other income	459	414	196
Total income	21,167	20,222	19,730
Expenses [Abstract]
Interest expense	1,417	1,170	1,131
Depreciation expense	107	130	153
Other expenses	2,256	2,465	2,550
Total expenses	3,780	3,765	3,834
Income before income taxes and equity in undistributed income of subsidiaries	17,387	16,457	15,896
Income tax benefit	(1,373)	(1,371)	(1,548)
Income before equity in undistributed income of subsidiaries	18,760	17,828	17,444
Equity in undistributed income of subsidiaries	28,586	28,604	25,807
Net income	47,346	46,432	43,251
Unrealized holding gains (losses) on securities available-for-sale [Abstract]
Unrealized holding gains (losses) arising during the period	(4,578)	(342)	13,928
Less: Reclassification adjustments for realized gains (losses) included in net income	522	(106)	(211)
Tax expense (benefit)	(1,785)	(83)	4,949
Other comprehensive income (loss), net of tax	(3,315)	(153)	9,190
Comprehensive income	$ 44,031	$ 46,279	$ 52,441