Income Taxes - Other Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Provision for undistributed earnings of our foreign subsidiaries	$ 0
State Administration of Taxation, China
Income Taxes [Line Items]
Period of recognition for deductible expenses or deferred tax assets	5 years
Increase in income tax expense due to write-off of deferred tax assets for social insurance and housing funds	$ 0	$ 0	$ 600,000