Income Taxes - Components of Net Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Increase (decrease) in valuation allowance	$ 1,000
Reduction of valuation allowance		$ 16,700
Deferred tax assets:
Domestic tax loss carryforwards	31,904		$ 31,974
Foreign tax loss carryforwards	6,177		6,098
Stock-based compensation	3,707		3,129
Tax credits	3,037		3,860
Operating lease liability			3,121
Lease incentive obligation	790		0
Other assets	2,242		2,062
Valuation allowance	(39,040)		(38,603)
Total deferred tax assets	8,817		11,641
Deferred tax liabilities:
Fixed assets	460		821
Intangible assets	557		491
Capitalized contract costs	3,898		4,468
Right of use assets			2,478
Deferred Tax Liabilities, Other	0		21
Total deferred tax liabilities	4,915		8,279
Net deferred tax asset	$ 3,902		$ 3,362