Income taxes - Provision For Income Taxes Charged To Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax expense:
U.S. federal	$ 18,212	$ 15,898	$ 91,043
State	2,705	2,963	348
Foreign	10,156	14,273	9,352
Total current	31,073	33,134	100,743
Deferred tax benefit:
U.S. federal	(9,168)	(10,724)	(4,796)
State	(1,218)	1,134	(151)
Foreign	(3,045)	(2,148)	(827)
Total deferred	(13,431)	(11,738)	(5,774)
Change in valuation allowance	751	0	0
Total provision	$ 18,393	$ 21,396	$ 94,969