Summary of Significant Accounting Policies - Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of adopting ASC 606	$ (5,511)
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of adopting ASC 606	(5,511)	$ (783)
Additional Paid-In Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of adopting ASC 606		$ 783
Accounting Standards Update 2016-09, Forfeiture Rate Component | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of adopting ASC 606	(800)
Accounting Standards Update 2016-09, Forfeiture Rate Component | Additional Paid-In Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of adopting ASC 606	$ 800