Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in cash flows from operating activities	$ 57,187	$ 22,600	$ 28,019
Decrease in cash flows from financing activities	(67,303)	(1,102)	(75,399)
Accumulated deficit	88,677	117,909
Additional paid-in capital	321,032	308,697
Deferred income tax assets	$ 18,424	16,752
Accounting Standards Update 2016-09, Statutory Tax Withholding Component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in cash flows from operating activities		5,100	900
Decrease in cash flows from financing activities		$ 5,100	$ 900
Accounting Standards Update 2016-09, Forfeiture Rate Component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit				$ 100
Additional paid-in capital				100
Deferred income tax assets				$ 100