Workers' Compensation Assets and Claim Liabilities - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Abstract]
Collateral held by insurance carriers	$ 65,600	$ 58,500	$ 95,400
Collateral paid to carriers and offset against loss reserves	$ (31,611)	$ (26,890)	$ (55,492)