Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Mar. 06, 2017 USD ($)	Dec. 30, 2016 € / shares
Class of Stock [Line Items]
Authorized share capital			$ 5,500,000
Ordinary shares, shares authorized (in shares) | shares	500,000,000	500,000,000	500,000,000
Ordinary shares, nominal value (in usd or euro per share) | (per share)	$ 0.01	$ 0.01	$ 0.01		€ 0.122
Preferred shares, shares authorized (in shares) | shares	50,000,000	50,000,000	50,000,000
Preferred shares, nominal value (in usd per share) | $ / shares	$ 0.01	$ 0.01	$ 0.01
Adjustment to reduce share premium				$ 317,254,000
Operating expenses	$ 208,195,000	$ 83,740,000	$ 155,211,000
Ordinary shares
Class of Stock [Line Items]
Cross-border merger nominal value adjustment			(5,937,000)
Advertising
Class of Stock [Line Items]
Operating expenses	$ 17,562,000	$ 2,214,000	$ 1,294,000