Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Percentage of customer revenue	45.00%	41.00%	40.00%
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	31.0
State of Nebraska [Member]
Workers' compensation insurance bonds	29.8
Workers' Compensation Insurance Carrier [Member]
Workers' compensation insurance bonds	$ 6.9