Summary of significant accounting policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Recent Accounting Pronouncements
Operating lease liabilities	$ 22,874
Financing lease liabilities	1,538
Retained earnings	$ (1,775,352)		$ (1,877,759)	[1]
Capital lease obligation			18,696
Office Building in Morges, Switzerland | Building and leasehold improvements
Recent Accounting Pronouncements
Capital lease asset			18,700
Capital lease obligation			$ 18,700
ASU No. 2016-02 | Restatement Adjustment
Recent Accounting Pronouncements
Financing lease assets		$ 23,600
Financing lease liabilities		23,700
Retained earnings		$ 100

[1] The condensed consolidated balance sheet at December 31, 2018 has been derived from the audited financial statements at that date.