Parent Company Only Financial Information (Statement of Cash Flow) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income	$ 9,001	$ 10,895	$ 9,766	$ 8,809	$ 7,408	$ 7,792	$ 7,962	$ 7,995	$ 38,471	$ 31,157	$ 10,941
Depreciation, amortization and accretion, net									18,142	19,169	18,503
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on investment securities	(764)	$ (1,861)	$ (18)	(340)	(68)	$ 1	$ (767)	(96)	(2,983)	(930)	(729)
Net cash provided by operating activities									60,820	60,311	47,882
Investing activities:
Business combinations, net of cash received									(1,069)	(244)	97,277
Net cash used in investing activities									(162,688)	(198,358)	(1,110)
Financing activities:
Payments on long-term borrowings									(5,738)	(24,361)	(72,446)
Purchase of treasury stock									5,000	4,965
Proceeds from issuance of common shares									9	18	0
Cash dividends paid									(14,706)	(11,173)	(10,065)
Excess tax benefit from share-based payments									0	26	51
Net cash provided by (used in) financing activities									107,916	133,078	(37,111)
Net increase (decrease) in cash and cash equivalents									6,048	(4,969)	9,661
Cash and cash equivalents at beginning of period				66,146				71,115	66,146	71,115	61,454
Cash and cash equivalents at end of period	72,194				66,146				72,194	66,146	71,115
Supplemental cash flow information:
Interest paid									12,880	10,439	11,541
Holding Company
Operating activities:
Net income									38,471	31,157	10,941
Depreciation, amortization and accretion, net									(6,525)	190	165
Adjustments to reconcile net income to net cash provided by operating activities:
Excess dividends from (equity in) undistributed earnings of subsidiaries									7,590	(12,162)	2,776
Gain on investment securities									(2,602)	0	0
Other, net									2,810	355	(1,903)
Net cash provided by operating activities									39,744	19,540	11,979
Investing activities:
Proceeds from Sale, Maturity and Collection of Investments									2,359
Investment in subsidiaries									(50,883)	(22,769)	(104,584)
Decrease (increase) in receivable from subsidiary									25,496	23,389	(2,860)
Business combinations, net of cash received									0		83,391
Payments for (Proceeds from) Other Investing Activities									(229)
Net cash used in investing activities									(23,257)	620	(24,053)
Financing activities:
Payments on long-term borrowings									0	0	(14,400)
Purchase of treasury stock									(508)	(5,480)	(741)
Proceeds from issuance of common shares									9	18	0
Cash dividends paid									(14,706)	(11,173)	(10,065)
Excess tax benefit from share-based payments									0	26	51
Net cash provided by (used in) financing activities									(15,205)	(16,609)	(25,155)
Net increase (decrease) in cash and cash equivalents									1,282	3,551	(37,229)
Cash and cash equivalents at the beginning of year					8,038					8,038	4,487	$ 41,716
Cash and cash equivalents at beginning of period				$ 8,038				$ 4,487	8,038	4,487
Cash and cash equivalents at end of period	$ 9,320				$ 8,038				9,320	8,038	4,487
Supplemental cash flow information:
Interest paid									$ 364	$ 433	$ 594