Income Tax Expense (Schedule of Components of Income Tax Expense) (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
Current tax expense:
Federal									$ 19,444	$ 17,864	$ 16,286
State									2,061	1,194	866
Total current tax expense									21,505	19,058	17,152
Deferred tax expense (benefit):
Federal									796	2,003	1,820
State									72	(183)	27
Total deferred tax expense									868	1,820	1,847
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