Segment information - Revenues by geography (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 102,543	$ 102,834
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	0	0
Italy
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1,318	2,217
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	8,591	7,662
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	23,384	19,010
Brazil
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	21,287	23,492
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 47,963	$ 50,453