Accounting Policies - VIE Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Current assets (VIE)	$ 29,847	$ 33,066
Non-current assets (VIE)	7,016	6,466
Current liabilities (VIE)	12,006	12,953
Non-current liabilities (VIE)	7,281	$ 8,780
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Variable Interest Entity [Line Items]
Disposal group, assets	8,100
Disposal group, liabilities	$ 6,300