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 period	$ 291	$ 425	$ 563
Additions charged to costs and expenses	109	92	47
Additions charged to other accounts	19	(61)	(90)
Deductions	1	(165)	(95)
Balance at end of period	420	291	425
Valuation allowance on deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	69,928	91,462	110,780
Additions charged to costs and expenses	4,876	16,320	4,573
Additions charged to other accounts	(4,563)	(37,854)	(23,891)
Deductions	0	0	0
Balance at end of period	$ 70,241	$ 69,928	$ 91,462