Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accounts Receivable Additional Disclosures [Abstract]
Trade receivables, allowance for doubtful accounts	$ 1,100	$ 1,200
Accounts receivable, due date prior to applicable payroll date	1 day
Unbilled accounts receivable [Abstract]
Accrued worksite employee payroll cost	$ 161,917	192,396
Unbilled revenues	45,835	55,645
Customer prepayments	(17,037)	(87,887)
Unbilled accounts receivable	$ 190,715	$ 160,154