Summary of Significant Accounting Policies - Merger Agreement (Details)	Sep. 30, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares	Mar. 06, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 30, 2016 € / shares
Accounting Policies [Abstract]
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 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
Distributable reserves, increase (decrease), adjustment			$ 317,254,000
Adjustment to reduce share premium			$ 317,254,000