Revenue - Sales by geographic region (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
Sales to external customers									100.00%	100.00%	100.00%
North America [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 373,634	$ 372,834	$ 377,347
Sales to external customers									47.40%	51.80%	56.20%
Asia [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 295,155	$ 250,574	$ 221,690
Sales to external customers									37.40%	34.90%	33.10%
Europe [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 119,427	$ 94,793	$ 71,796
Sales to external customers									15.10%	13.20%	10.70%
Other [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 732	$ 691	$ 179
Sales to external customers									0.10%	0.10%