Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Taxes [Line Items]
United States statutory tax rate	35.00%	21.00%	24.50%	35.00%	35.00%
Decrease in deferred tax asset due to Tax Act		$ 8,100
Cash and cash equivalents held by foreign subsidiaries		7,300	$ 7,300
Temporary difference related to undistributed earnings		12,900	12,900	$ 12,800
Valuation allowance against net deferred tax assets			(4,237)	20,087	$ 7,715
United States
Income Taxes [Line Items]
Net operating loss, carryforwards		62,200	62,200	$ 49,400
Net operating loss, carryforwards expiration year				2028
Tax Cuts And Jobs Act Of 2017, change in tax rate income tax expense benefit			12,800
Valuation allowance against net deferred tax assets			20,900	$ 23,600
Canada
Income Taxes [Line Items]
Net operating loss, carryforwards		14,000	$ 14,000
Net operating loss, carryforwards expiration year			2033
Valuation allowance against net deferred tax assets			$ 4,400	$ 4,700
Russia
Income Taxes [Line Items]
Net operating loss, carryforwards		$ 600	$ 600
Net operating loss, carryforwards expiration year			2026