Workers Compensation - Summary of Activities in Liability for Unpaid Claims and Claims Adjustment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Liability for Unpaid Claims and Claims Adjustment Expense
Liability for unpaid claims and claims adjustment at beginning of period	$ 190,102	$ 148,034
Incurred related to:
Current year	22,774	89,137
Prior years	5,263	26,391
Total incurred	28,037	115,528
Paid related to:
Current year	(711)	(16,376)
Prior years	(17,276)	(57,084)
Total paid	(17,987)	(73,460)
Liability for unpaid claims and claims adjustment at end of period	200,152	190,102
Assets held by third parties to cover claim liabilities	(67,807)	(58,522)
Workers compensation premiums and other liabilities	16,000	9,455
Other workers compensation assets	(6,471)	(1,012)
Total net workers compensation liabilities	141,874	140,023
Current portion included in worksite employee-related liability	61,100	66,174
Long term portion	119,900	105,481
Workers' Compensation Liability	181,000	171,655
Current portion included in worksite employee-related asset	2,234	2,428
Long term portion	36,892	29,204
Workers Compensation Receivable, Total	$ 39,126	$ 31,632