Parent Company Financial Statements (Condensed Statements of Cash Flows) (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
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income	$ 11,621	$ 9,660	$ 9,839	$ 9,556	$ 10,065	$ 10,185	$ 9,788	$ 5,146	$ 40,676	$ 35,184	$ 30,064
Adjustments to Reconcile Net Income to Net Cash from Operations
Interest Receivable and Other Assets									(4,528)	5,813	172
Change in Other Liabilities									(110)	(2,547)	(1,328)
Equity Based Compensation									1,246	1,407	963
Excess Tax Benefit from Restricted Share Grant									240	200	89
Net Cash from Operating Activities									54,875	41,913	31,267
CASH FLOWS FROM INVESTING ACTIVITIES
Cash Used for Business Acquisitions									0	(1,016)	0
Net Cash from Investing Activities									(189,280)	(71,689)	(126,929)
CASH FLOWS FROM FINANCING ACTIVITIES
Repayment of Long-term Debt									(53,864)	(24,910)	(44,135)
Issuance (Retirement) of Common Stock									(29)	55	49
Employee Stock Purchase Plan											447
Dividends Paid									(11,842)	(10,630)	(9,010)
Net Cash from Financing Activities									139,948	42,583	105,225
Net Change in Cash and Cash Equivalents									5,543	12,807	9,563
Cash and Cash Equivalents at Beginning of Year				64,816				52,009	64,816	52,009	42,446
Cash and Cash Equivalents at End of Year	70,359				64,816				70,359	64,816	52,009
Parent Company
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income									40,676	35,184	30,064
Adjustments to Reconcile Net Income to Net Cash from Operations
Interest Receivable and Other Assets									431	2,085	(5,331)
Change in Other Liabilities									(122)	310	1,226
Equity Based Compensation									1,246	1,407	963
Excess Tax Benefit from Restricted Share Grant									240	200	89
Equity in Excess Undistributed Income of Subsidiaries									(16,040)	(21,514)	(14,111)
Net Cash from Operating Activities									26,431	17,672	12,900
CASH FLOWS FROM INVESTING ACTIVITIES
Cash Used for Business Acquisitions									0	(15,992)	0
Net Cash from Investing Activities									0	(15,992)	0
CASH FLOWS FROM FINANCING ACTIVITIES
Repayment of Long-term Debt									0	0	(4,000)
Issuance (Retirement) of Common Stock									(29)	55	49
Employee Stock Purchase Plan											447
Dividends Paid									(11,842)	(10,630)	(9,010)
Net Cash from Financing Activities									(11,871)	(10,575)	(12,514)
Net Change in Cash and Cash Equivalents									14,560	(8,895)	386
Cash and Cash Equivalents at Beginning of Year				$ 10,217				$ 19,112	10,217	19,112	18,726
Cash and Cash Equivalents at End of Year	$ 24,777				$ 10,217				$ 24,777	$ 10,217	$ 19,112