Income Taxes (Schedule of Income Tax Expense) (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
Current:
Federal									$ 14,529	$ 17,854	$ 7,956
State									1,289	930	71
Total									15,818	18,784	8,027
Deferred:
Change in federal corporate income tax rate(1)									14,263	0	0
Federal									4,117	(1,258)	1,356
Deferred State and Local Income Tax Expense (Benefit)									(320)	(54)	524
Deferred Income Tax Expense (Benefit)									18,060	(1,312)	1,880
Income tax expense	$ 19,335	$ 5,478	$ 4,721	$ 4,344	$ 4,730	$ 5,042	$ 4,258	$ 3,442	$ 33,878	$ 17,472	$ 9,907