Basis of Presentation - Recently Adopted Accounting Standards (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash paid on behalf of employees for shares withheld	$ 5,027	$ 5,124
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease commitment	$ 25,200