Recently issued accounting standards Recently issued accounting standards (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Debt Issuance Costs, Net	$ 10,046	$ 6,742
Prepaid expenses and other current assets | Accounting Standards Update 2015-03 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt Issuance Costs, Net		(2,600)
Other current liabilities | Accounting Standards Update 2015-03 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt Issuance Costs, Net		2,600
Other Assets | Accounting Standards Update 2015-03 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt Issuance Costs, Net		(4,200)
Long-term Debt | Accounting Standards Update 2015-03 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt Issuance Costs, Net		$ 4,200