Cash Equivalents and Marketable Securities - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
		Dec. 31, 2009	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Jan. 01, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents			$ 93,421	$ 53,621	$ 93,421	$ 53,621	$ 53,039
Cash, cash equivalents, and short-term investments			73,586		73,586		31,813
Percentage of outstanding shares owned at time of investment		16.60%
Statutory resale restriction expiry period		4 months
Effect of new accounting principle	[1]							$ (4,060)
Unrealized gains (losses)					(168)	5
Other Expense [Member]
Cash and Cash Equivalents [Line Items]
Unrealized gains (losses)			(64)	$ (20)	(200)	$ 5
Accounting Standards Update 2016-01 [Member]
Cash and Cash Equivalents [Line Items]
Effect of new accounting principle								$ 500
Common Shares of Co Two Solution [Member]
Cash and Cash Equivalents [Line Items]
Number of common shares fair value		10,000,000
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents			73,167		73,167		31,225
Cash, cash equivalents, and short-term investments			73,200		73,200		31,200
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents, and short-term investments			$ 20,200		$ 20,200		$ 21,800

[1] (1) Cumulative effect of change in accounting principles included: Accounting Standards Update 2014-9 (Topic 606), of $4.1 million and Accounting Standards Update 2016-01 (Subtopic 825-10), of $0.5 million.