New accounting standards (Details 11) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax expense (benefit), continuing operations, adjustment of deferred tax (asset) liability	$ (39,500)	$ 7,735	$ 0	$ 0
Other comprehensive income (loss) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax expense (benefit), continuing operations, adjustment of deferred tax (asset) liability	7,700
Adjustments for New Accounting Pronouncement [Member] | Other comprehensive income (loss) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax expense (benefit), continuing operations, adjustment of deferred tax (asset) liability	$ 7,700