Worksite Employee-Related Assets and Liabilities - Schedule of Components of the Company's WSE-Related Assets and WSE-Related Liabilities (Details) $ in Thousands	Sep. 30, 2016 USD ($) employee	Dec. 31, 2015 USD ($)
Worksite employee-related assets:
Restricted cash	$ 14,563	$ 14,557
Total worksite employee-related assets	847,545	1,373,386
Worksite employee-related liabilities:
Health benefits payable	29,039	28,963
Workers compensation payable	64,432	66,174
Total worksite employee-related liabilities	$ 842,552	1,369,497
Number of employees | employee	2,500
WSE
Worksite employee-related assets:
Restricted cash	$ 113,934	92,917
Restricted investments	2,319	3,819
Payroll funds collected	442,329	859,322
Unbilled revenue, net of advance collections of $5,504 and $11,875 at September 30, 2016 and December 31, 2015, respectively	268,480	213,837
Accounts receivable, net of allowance for doubtful accounts of $430 and $1,158 at September 30, 2016 and December 31, 2015, respectively	4,701	5,060
Prepaid health plan expenses	6,692	8,088
Workers compensation receivables	1,860	2,428
Prepaid workers compensation expenses	3,057	744
Other payroll assets	4,173	187,171
Total worksite employee-related assets	847,545	1,373,386
Advance collection	5,504	11,875
Allowance for doubtful accounts	430	1,158
Worksite employee-related liabilities:
Unbilled wages accrual	254,267	202,396
Payroll taxes payable	312,097	883,608
Health benefits payable	131,038	128,028
Customer prepayments	38,143	57,758
Workers compensation payable	64,432	66,174
Other payroll deductions	42,575	31,533
Total worksite employee-related liabilities	$ 842,552	1,369,497
Customer One
Worksite employee-related assets:
Payroll funds collected		$ 181,000