Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 171	$ 171
Addition charged to costs and expenses	0	0
Other additions (deductions)	0	0
Less deductions	0	0
Balance at end of year	171	171
Deferred tax asset valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	71,208	88,934
Addition charged to costs and expenses	17,492	0
Other additions (deductions)	0	2,842
Less deductions	(35,218)	0
Balance at end of year	$ 88,934	$ 86,092