Parent Only Financial Information Parent Only Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Interest and Dividends on Investments	$ 84,657	$ 76,915	$ 70,738
Other Operating Income	927	1,113	1,354
Interest Expense	7,006	5,356	4,813
Salaries and Employee Benefits	37,166	34,330	33,064
Other Operating Expense	15,088	14,801	13,913
Provision for Income Taxes	10,529	11,215	10,610
Net Income	29,326	26,534	24,662
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends from Bank Subsidiaries	12,800	11,650	13,400
Interest and Dividends on Investments	53	117	118
Other Operating Income	677	635	847
Total Income	13,530	12,402	14,365
Interest Expense	781	691	619
Salaries and Employee Benefits	76	77	80
Other Operating Expense	882	865	885
Total Expense	1,739	1,633	1,584
Income Before Income Tax Benefit and Equity in Undistributed Net Income of Subsidiaries	11,791	10,769	12,781
Provision for Income Taxes	225	482	372
Equity in Undistributed Net Income of Subsidiaries	17,310	15,283	11,509
Net Income	$ 29,326	$ 26,534	$ 24,662