Parent Company Financial Statements, Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities [Abstract]
Net income	$ 47,346	$ 46,432	$ 43,251
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Depreciation	3,904	3,932	4,314
Stock-based compensation	458	783	852
Excess tax benefits of stock-based compensation	100	104	760
Changes in [Abstract]
Other assets	(3,205)	(6,274)	(60)
Other liabilities	2,874	(2,488)	(1,339)
Net cash provided by operating activities	61,425	54,979	57,528
Cash flows from investing activities [Abstract]
Purchase of premises and equipment	(3,498)	(2,246)	(2,081)
Net cash used in investing activities	(86,107)	(108,349)	(144,076)
Cash flows from financing activities [Abstract]
Issuance of common stock	2,985	2,082	1,992
Repurchase of common stock	(382)	(189)	0
Excess tax benefits of stock-based compensation	(100)	(104)	(760)
Dividends paid	(22,190)	(21,330)	(20,570)
Net cash provided by (used in) financing activities	(18,213)	135,464	85,424
Net increase (decrease) in cash and cash equivalents	(42,895)	82,094	(1,124)
Cash and cash equivalents at beginning of year	187,611	105,517	106,641
Cash and cash equivalents at end of year	144,716	187,611	105,517
Parent Company [Member]
Cash flows from operating activities [Abstract]
Net income	47,346	46,432	43,251
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Depreciation	107	130	153
Equity in undistributed earnings of subsidiaries	(28,586)	(28,604)	(25,807)
Stock-based compensation	458	783	838
Excess tax benefits of stock-based compensation	100	104	760
Changes in [Abstract]
Other assets	519	240	(558)
Other liabilities	(90)	968	563
Net cash provided by operating activities	19,854	20,053	19,200
Cash flows from investing activities [Abstract]
Purchase of premises and equipment	(104)	(45)	(125)
Repayment of investments in and advances to subsidiaries	0	0	(14)
Net cash used in investing activities	(104)	(45)	(139)
Cash flows from financing activities [Abstract]
Issuance of common stock	2,985	2,082	1,992
Repurchase of common stock	(382)	(189)	0
Excess tax benefits of stock-based compensation	(100)	(104)	(760)
Dividends paid	(22,190)	(21,330)	(20,570)
Net cash provided by (used in) financing activities	(19,687)	(19,541)	(19,338)
Net increase (decrease) in cash and cash equivalents	63	467	(277)
Cash and cash equivalents at beginning of year	1,462	995	1,272
Cash and cash equivalents at end of year	$ 1,525	$ 1,462	$ 995