Income Taxes - Income Tax Expense (Benefit), Continuing Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax expense:
Federal	$ 15,060	$ 16,677	$ 22,265
State	3,244	3,829	4,632
Deferred tax expense	12,505	2,676	1,951
Income tax expense (benefit)	$ 30,809	$ 23,182	$ 28,848