Revenue - Net sales by extended warranty and service contracts (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 338,268	$ 175,127	$ 134,810	$ 140,743	$ 154,161	$ 173,082	$ 196,032	$ 195,617	$ 788,948	$ 718,892	$ 671,012
Product and service revenue recognized at point in time
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									786,918	715,055	667,440
Extended warranty and service contracts recognized over time
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 2,030	$ 3,837	$ 3,572