Income Taxes - Income Tax Expense (Benefit) Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax at the statutory federal rate	$ 14,594	$ 8,065	$ (323)
State income taxes (net of federal benefit)	1,340	806	(32)
Decrease in valuation allowance, net	(142)	(941)	(164)
Fees and expenses for SEC investigation	0	0	1,092
Change in statutory federal rate to 21%	(33,542)	0	0
Dividend received deduction	(530)	(40)	0
Other	399	(743)	235
Total income tax (benefit) expense	$ (17,881)	$ 7,147	$ 808