Schedule V. Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for bad debts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 1,255	$ 867	$ 618
Charged to costs and expenses	0	388	249
Deductions	0	0	0
Balance at end of period	1,255	1,255	867
Deferred tax asset valuation allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	718	1,265	1,813
Charged to costs and expenses	0	0	0
Deductions	389	547	548
Balance at end of period	$ 329	$ 718	$ 1,265