Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves
Balance at beginning of period	$ 544	$ 420	$ 291
Additions charged to costs and expenses	69	181	109
Additions charged to other accounts	(43)	33	19
Deductions	(31)	(90)	1
Balance at end of period	539	544	420
Valuation allowance on deferred tax assets
Movement in Valuation Allowances and Reserves
Balance at beginning of period	49,337	70,241	69,928
Additions charged to costs and expenses	5,547	2,215	4,876
Additions charged to other accounts	(3,933)	(23,119)	(4,563)
Deductions	0	0	0
Balance at end of period	$ 50,951	$ 49,337	$ 70,241