Parent Company Financial Information, 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 [Abstract]
Net Income	$ 3,781	$ 8,581	$ 8,187	$ 7,821	$ 7,681	$ 7,538	$ 7,332	$ 7,172	$ 28,370	$ 29,723	$ 27,392
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Net Cash Provided by Operating Activities									39,944	34,812	37,327
Investing Activities [Abstract]
Net Cash Used in Investing Activities									(82,190)	(185,444)	(258,308)
Financing Activities [Abstract]
Cash Dividends									(10,982)	(10,478)	(10,157)
Net Cash Provided by (Used in) Financing Activities									130,535	190,046	203,302
Increase (Decrease) in Cash and Cash Equivalents									88,289	39,414	(17,679)
Parent Company [Member]
Cash Flows from Operating Activities [Abstract]
Net Income									28,370	29,723	27,392
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Equity in Undistributed Net Earnings from Subsidiary									(5,575)	(17,043)	(17,352)
Net (Increase) Decrease in Other Assets									(11,822)	(124)	(79)
Net Increase (Decrease) in Liabilities									112	49	141
Net Cash Provided by Operating Activities									11,085	12,605	10,102
Investing Activities [Abstract]
Securities Sold or Matured									1	0	0
Payments for Business Acquisition									0	(2,207)	0
Payments for Investments in Subsidiaries									(2,953)	(2,586)	(3,360)
Net Cash Used in Investing Activities									(2,952)	(4,793)	(3,360)
Financing Activities [Abstract]
Issuance of Common Stock									2,953	2,586	3,360
Cash Dividends									(10,982)	(10,478)	(10,157)
Net Cash Provided by (Used in) Financing Activities									(8,029)	(7,892)	(6,797)
Increase (Decrease) in Cash and Cash Equivalents									104	(80)	(55)
Cash and Cash Equivalents at Beginning of Year				$ 228				$ 308	228	308	363
Cash and Cash Equivalents at End of Year	$ 332				$ 228				$ 332	$ 228	$ 308