Parent Company Financial Statements (Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 12,162	$ 12,327	$ 11,057	$ 10,935	$ 10,744	$ 10,208	$ 11,503	$ 11,010	$ 46,481	$ 43,465	$ 40,824
Adjustments to reconcile net income to net cash provided by operating activities:
Decrease (increase) in other assets									(630)	4,458	8,250
Change in fair value of contingent consideration									(898)	41	0
Net cash provided by operating activities									58,733	51,566	2,648
Cash flows from investing activities:
Cash used in business combination, net of cash acquired									0	(1,671)	0
Net cash used in investing activities									(625,377)	(165,885)	(357,372)
Cash flows from financing activities:
Proceeds from stock option exercises and issuance of other equity instruments									977	1,563	1,189
Tax benefit from stock option exercises and other equity instruments									1,016	694	578
Cash dividends paid									(24,637)	(22,770)	(19,722)
Net cash provided by financing activities									576,810	131,600	349,757
Net increase (decrease) in cash and cash equivalents									10,166	17,281	(4,967)
Cash and cash equivalents at beginning of year				97,631				80,350	97,631	80,350	85,317
Cash and cash equivalents at end of year	107,797				97,631				107,797	97,631	80,350
Parent Company [Member]
Cash flows from operating activities:
Net income									46,481	43,465	40,824
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiary									(21,912)	(21,104)	(21,554)
(Increase) decrease in dividend receivable									(1,436)	19	(495)
Decrease (increase) in other assets									45	(67)	183
(Decrease) increase in accrued expenses and other liabilities									(12)	2,425	(516)
Change in fair value of contingent consideration									(898)	41	0
Other, net									(1,051)	(3,363)	(245)
Net cash provided by operating activities									21,217	21,416	18,197
Cash flows from investing activities:
Cash used in business combination, net of cash acquired									0	(1,671)	0
Net cash used in investing activities									0	(1,671)	0
Cash flows from financing activities:
Proceeds from stock option exercises and issuance of other equity instruments									978	1,563	1,189
Tax benefit from stock option exercises and other equity instruments									1,016	694	578
Cash dividends paid									(24,637)	(22,770)	(19,722)
Net cash provided by financing activities									(22,643)	(20,513)	(17,955)
Net increase (decrease) in cash and cash equivalents									(1,426)	(768)	242
Cash and cash equivalents at beginning of year				$ 3,169				$ 3,937	3,169	3,937	3,695
Cash and cash equivalents at end of year	$ 1,743				$ 3,169				$ 1,743	$ 3,169	$ 3,937