Income Taxes - Summary of Income Tax Expense Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current
Federal	$ 667	$ 653	$ 578
State	2	30	61
Deferred
Federal	32,791	12,163	10,818
State	2,876	2,043	2,070
Total income tax provision	$ 36,336	$ 14,889	$ 13,527