Fair value measurements (Derivatives Offset in the Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Derivative assets, gross		$ 14,483
Derivative assets, amount offset		(363)
Derivative assets		14,120
Derivative assets, not offset	[1]	0
Credit facility balance available to offset net derivative assets		(14,120)
Derivative asset, net		0
Derivative liabilities, gross		(363)
Derivative liabilities, amounts offset		363
Derivative liabilities, not offset	[1]	0
Credit facility balance available to offset net derivative liabilities		0
Derivative Asset (Liability), Fair Value, Gross Asset		14,120
Derivative Asset (Liability), Fair Value, Gross Liability		0
Derivative Asset (Liability), Net		14,120
Derivative liability asset not offset	[1]	$ 0
Predecessor
Offsetting Assets [Line Items]
Derivative assets, gross			$ 184
Derivative assets, amount offset			(184)
Derivative assets, not offset	[1]		0
Credit facility balance available to offset net derivative assets			0
Derivative asset, net			0
Derivative liabilities, gross			(13,553)
Derivative liabilities, amounts offset			184
Derivative liabilities			(13,369)
Derivative liabilities, not offset	[1]		0
Credit facility balance available to offset net derivative liabilities			0
Derivative liability, net			(13,369)
Derivative Asset (Liability), Fair Value, Gross Asset			(13,369)
Derivative Asset (Liability), Fair Value, Gross Liability			0
Derivative Asset (Liability), Net			(13,369)
Derivative liability asset not offset	[1]		0
Derivative asset (liability), net			$ (13,369)

[1] Since positive and negative positions with a counterparty are netted on the balance sheet only to the extent that they relate to the same current versus noncurrent classification, these represent remaining amounts that could have been offset under our master netting agreements.