Income Tax Expense (Schedule of Income Tax Rate Reconciliation) (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
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Tax expense at Federal statutory rate									$ 24,099	$ 22,520	$ 20,938
(Decrease) increase in taxes resulting from:
Tax-exempt income									(1,599)	(1,604)	(1,540)
Dividends received deduction									(58)	(57)	(29)
BOLI									(930)	(694)	(646)
Federal tax credits									(364)	(364)	(364)
Income Tax Reconciliation Change in fair value of contingent consideration									(314)	0	0
Acquisition related expenses									0	318	0
State income tax expense, net of federal income tax benefit									1,387	658	581
Other									152	101	59
Total income tax expense	$ 5,873	$ 5,863	$ 5,153	$ 5,484	$ 5,346	$ 4,964	$ 5,387	$ 5,181	$ 22,373	$ 20,878	$ 18,999