Income Taxes Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax expense:
Federal	$ 19,553	$ 33,872	$ 34,455
State	2,617	1,698	2,042
Total	22,170	35,570	36,497
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	39,885	7,968	12,752
State	646	3,086	672
Total	40,531	11,054	13,424
Income tax expense	$ 62,701	$ 46,624	$ 49,921