Description of Business and Significant Accounting Policies - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash used in financing activities	$ (45,141)	$ (36,230)
Net cash provided by operating activities	$ 104,113	43,667
Number of reportable segments as result of acquisitions | segment	1
Restricted cash, cash equivalents and payroll funds collected	$ 741,100		$ 1,000,000
Accounting Standards Update 2016-09, Statutory Tax Withholding Component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash used in financing activities		(700)
Net cash provided by operating activities		$ 700
Retained Earnings | Accounting Standards Update 2016-09, Forfeiture Rate Component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment			$ 300