Income taxes - Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal	$ (2,925)	$ 18,548	$ 55,846
State	(356)	3,007	6,075
Foreign	8,542	6,539	8,219
Total current	5,261	28,094	70,140
Deferred:
Federal	37,573	(11,211)	(13,551)
State	4,436	(204)	(3,369)
Foreign	(3,441)	(225)	(333)
Total deferred	38,568	(11,640)	(17,253)
Income tax expense	$ 43,829	$ 16,454	$ 52,887