Segment Reporting - Regional long-lived assets by country (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Long-lived assets	$ 4,872,364	$ 4,989,083
Operating Segments | United States
Segment Reporting Information [Line Items]
Long-lived assets	2,165,662	2,178,142
Operating Segments | United Kingdom
Segment Reporting Information [Line Items]
Long-lived assets	2,685,784	2,799,392
Operating Segments | Other countries
Segment Reporting Information [Line Items]
Long-lived assets	$ 20,918	$ 11,549