Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating losses	$ 23,490	$ 18,771
Capitalized inventory costs	4,581	12,378
Stock based compensation	3,793	6,955
Accruals not currently deductible	7,730	4,883
Unrealized foreign exchange losses, net	2,595	3,087
Foreign tax credits	9,262	3,269
Other	10,451	1,871
Total deferred tax assets	61,902	51,214
Valuation allowance	(30,154)	(21,847)
Total deferred tax assets, net of allowances	31,748	29,367
Deferred tax liabilities:
Accelerated depreciation and amortization	(34,265)	(43,225)
Original issue discount on 2021 Convertible Notes	(4,299)	(8,553)
Tax on unremitted earnings	(16,821)	(8,555)
Other	(3,190)	(6,030)
Total deferred tax liabilities	(58,575)	(66,363)
Total net deferred tax liabilities	(26,827)	(36,996)
Non-current deferred tax assets	4,753	1,747
Non-current deferred tax liabilities	(31,580)	(38,743)
Net deferred tax liabilities	$ (26,827)	$ (36,996)