Business Combinations - Transaction Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Transaction Costs
Equity issuance costs	$ 7,649
Debt issuance costs	40,900
HGM
Transaction Costs
Contract cancellation and advising fees	23,000
Novitex Business Combination
Transaction Costs
Transaction costs	$ 60,000