Leases - Prepaid Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) factory	Dec. 31, 2016 USD ($)
Operating Leased Assets [Line Items]
Net book value of asset	$ 110,962	$ 105,351
People's Republic of China (PRC)
Operating Leased Assets [Line Items]
Number of factories | factory	1
Net book value of asset	$ 93,600	$ 90,000
Yangzhou
Operating Leased Assets [Line Items]
Net book value of prepaid lease	$ 2,600
Prepaid lease assets, remaining amortization period	41 years
Yangzhou | Buildings on Prepaid Land
Operating Leased Assets [Line Items]
Net book value of asset	$ 20,900
Asset, remaining depreciable period	22 years