Worksite Employee-Related Assets and Liabilities - Schedule of Components of the Company's WSE-Related Assets and WSE-Related Liabilities (Details) $ in Thousands	Dec. 31, 2015 USD ($) employee	Dec. 31, 2014 USD ($)
Worksite employee-related assets:
Restricted cash	$ 14,557	$ 14,543
Prepaid health plan expenses	6,800	4,900
Total worksite employee-related assets	1,373,386	1,635,136
Worksite employee-related liabilities:
Health benefits payable	28,963	29,179
Workers compensation payable	66,174	36,778
Total worksite employee-related liabilities	$ 1,369,497	1,630,555
Entity Number of Employees | employee	2,500
WSE
Worksite employee-related assets:
Restricted cash	$ 92,917	64,890
Restricted investments	3,819	4,555
Payroll funds collected	859,322	1,336,994
Unbilled revenue, net of advance collections of $11,875 and $113,190 at December 31, 2015 and December 31, 2014, respectively	213,837	203,599
Accounts receivable, net of allowance for doubtful accounts of $1,158 and $388 at December 31, 2015 and December 31, 2014, respectively	5,060	5,193
Prepaid health plan expenses	8,088	4,932
Prepaid workers compensation expenses	744	1,256
Other payroll assets	187,171	5,742
Total worksite employee-related assets	1,373,386	1,635,136
Advance collection	11,875	113,190
Allowance for doubtful accounts	1,158	388
Worksite employee-related liabilities:
Unbilled wages accrual	202,396	292,906
Payroll taxes payable	883,608	1,119,427
Health benefits payable	128,028	104,220
Customer prepayments	57,758	53,770
Workers compensation payable	66,174	36,778
Other payroll deductions	31,533	23,454
Total worksite employee-related liabilities	1,369,497	1,630,555
WSE | Workers compensation
Worksite employee-related assets:
Refundable workers compensation premiums	2,428	$ 7,975
Customer One | WSE
Worksite employee-related assets:
Payroll funds collected	$ 181,000