Recently issued accounting standards (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets	$ 112,278
Operating lease liabilities	$ 121,053
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets		$ 105,300
Operating lease liabilities		$ 106,600