BUSINESS COMBINATION - CONSIDERATION PAID (Details)		3 Months Ended		6 Months Ended
	May 29, 2015 USD ($) $ / shares	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) payment	Jun. 30, 2015 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Assets acquired and liabilities assumed
Multi-employer withdrawal liabilities		$ (60,900,000)		$ (60,900,000)			$ (56,200,000)
Goodwill		245,100,000	$ 241,600,000	245,100,000	$ 241,600,000	$ 241,600,000	$ 241,600,000	$ 27,400,000	$ 27,400,000
Interest Expense		6,500,000	4,600,000	11,400,000	8,900,000
Horizon
Business acquisition
Business Combination, Ownership Percentage	100.00%
Cash price (in dollars per share) | $ / shares	$ 0.72
Assets acquired and liabilities assumed
Cash and cash equivalents		800,000		800,000
Accounts receivable		31,700,000		31,700,000
Other current assets		7,200,000		7,200,000
Deferred tax assets, net		46,300,000		46,300,000
Property and equipment		170,400,000		170,400,000
Intangibles - Customer relationships		140,000,000		140,000,000
Other long-term assets		4,100,000		4,100,000
Accounts payable		(22,800,000)		(22,800,000)
Accruals and other current liabilities		(31,400,000)		(31,400,000)
Multi-employer withdrawal liabilities	$ (60,600,000)	(65,500,000)		(65,500,000)
Capital lease obligations		(1,600,000)		(1,600,000)
Horizon's debt and warrants		(467,500,000)		(467,500,000)
Total identifiable assets less liabilities		(188,300,000)		(188,300,000)
Total cash paid for common shares				(29,400,000)
Goodwill		217,700,000		217,700,000
Estimated future benefit payments
Mass withdrawal liability undiscounted payments		102,000,000		$ 102,000,000
Benefit payment period (in quarters) | payment				98
Quarterly payments to ILA-PRSSA over an estimated period		1,036,647		$ 1,036,647
Incremental borrowing rate				3.87%
Horizon | As previously Reported
Total cash consideration
Common shares	29,400,000
Warrants	37,100,000
Horizon's debt (including accrued interest and breakage fees)	428,900,000
Total	$ 495,400,000
Horizon | Adjustments
Assets acquired and liabilities assumed
Deferred tax assets, net		700,000		$ 700,000
Accruals and other current liabilities		700,000		700,000
Multi-employer withdrawal liabilities		(4,900,000)		(4,900,000)
Total identifiable assets less liabilities			$ 2,000,000		$ 2,000,000
Goodwill		3,500,000		3,500,000
Interest Expense		$ 1,100,000		$ 1,100,000