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Goodwill and other intangible assets - Additional Information (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]      
Depreciation and amortization $ 7,100,000 $ 7,100,000 $ 8,300,000
Impairment of finite-lived intangible assets $ 0