Fair Value Measurements - Schedule of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 54,225	$ 23,826	$ 54,225	$ 23,826	$ 31,219
Equity securities, estimated fair value	652		652
Equity securities					671
Summary of financial instruments measured at fair value on a recurring basis
Financial assets	31,710		31,710		7,449
Unrealized gains (losses)			(20)	0
Other Expense [Member]
Summary of financial instruments measured at fair value on a recurring basis
Unrealized gains (losses)	(25)		(20)
Other Comprehensive Income (Loss) [Member]
Summary of financial instruments measured at fair value on a recurring basis
Unrealized gains (losses)		$ 100		$ (21)
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	31,058		31,058		6,778
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, estimated fair value	0		0
Equity securities					0
Summary of financial instruments measured at fair value on a recurring basis
Financial assets	31,058		31,058		6,778
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	31,058		31,058		6,778
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, estimated fair value	652		652
Equity securities					671
Summary of financial instruments measured at fair value on a recurring basis
Financial assets	$ 652		$ 652		671
Level 2 [Member] | Common Shares of Co Two Solution [Member]
Summary of financial instruments measured at fair value on a recurring basis
Investment owned (in shares)	10,000,000		10,000,000
Level 2 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 0		$ 0		0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, estimated fair value	0		0
Equity securities					0
Summary of financial instruments measured at fair value on a recurring basis
Financial assets	0		0		0
Level 3 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 0		$ 0		$ 0