Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 171	$ 171	$ 161
Addition charged to costs and expenses	0	10	0
Other additions (deductions)	0	0	(5)
Less deductions	0	0	0
Balance at end of year	171	161	166
Deferred tax asset valuation allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	88,934	86,092	72,104
Addition charged to costs and expenses	0	0	0
Other additions (deductions)	2,842	13,988	6,272
Less deductions	0	0	0
Balance at end of year	$ 86,092	$ 72,104	$ 65,832