Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Percentage of customer revenue	43.00%	45.00%	41.00%
Accounts receivable recorded investment past due days	90
Self insurance retention liability	$ 2.0	$ 2.0	$ 2.0
Self insurance retention Workers' compensation	1.0
Letters of credit outstanding, amount	25.8
Reclassification of Deferred Tax Asset [Member]
Prior period reclassification adjustment	28.0
State of Nebraska [Member]
Workers' compensation insurance bonds	27.3
Workers' Compensation Insurance Carrier [Member]
Workers' compensation insurance bonds	$ 6.9