Summary of Significant Accounting Policies - Recently Adopted 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]
Deferred tax assets	$ 31,661	$ 47,801
Excess tax benefit	600
Valuation allowance	1,076	46,454
Share-based compensation	(4,100)	$ (3,400)	$ (2,500)
ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets				$ 1,300
Valuation allowance				1,300
Share-based compensation	$ 200
Retained Earnings | ASU 2016-09, Forfeiture Rate Component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment				$ 500