Acquisition of Gordon Trucking, Inc. (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Nov. 01, 2016	Dec. 31, 2015	Nov. 01, 2015	Dec. 31, 2014	Nov. 11, 2013
Business Acquisition [Line Items]
business combination contingent consideration fair value non-current			$ 12,200		$ 11,300
business combination contingent consideration fair value current					$ 2,300
Total acquisition purchase price	$ 300,000
Payments to Acquire Intangible Assets	15,000
Fair Value of Stock in Escrow Related To Acquisition of Business						$ 24,000
Fair Value of Cash in Escrow as a Result of Business Combination						6,000
Noncash or Part Noncash Acquisition, Debt Assumed	148,000
Line of Credit Facility, Maximum Borrowing Capacity		$ 175,000		$ 200,000		250,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High			$ 20,000			$ 20,000
Cash Acquired from Acquisition	20,000
Business Combination, Acquisition Related Costs	2,200
Gordon Trucking Company, Inc [Member]
Business Acquisition [Line Items]
Total acquisition purchase price	$ 285,000