Segment information - Revenues and long-lived assets by location of property (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	[1]	$ 549,824	$ 551,385	$ 585,715
Total property, plant and equipment at book value		1,074,676	1,078,361
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue		0	0	0
Total property, plant and equipment at book value		0	0
Italy
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue		128,671	132,385	137,491
Total property, plant and equipment at book value		294,773	308,035
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue		56,016	62,656	68,412
Total property, plant and equipment at book value		48,577	57,443
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue		108,238	107,965	104,146
Total property, plant and equipment at book value		343,342	346,942
Brazil
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue		73,300	69,142	86,866
Total property, plant and equipment at book value		73,843	61,773
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue		183,599	179,237	$ 188,800
Total property, plant and equipment at book value		$ 314,141	$ 304,168

[1] Includes revenue from related parties of $15,458,000, $13,123,000 and $12,988,000, respectively