Consolidated Balance Sheets (Parenthetical) $ in Thousands	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2018 € / shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2017 € / shares
Current assets:
Accounts receivable, allowances | $	$ 534		$ 4,162
Shareholders’ equity:
Ordinary shares, nominal value (in dollars per share) | $ / shares	$ 0.0001		$ 0.0001
Ordinary shares, authorized (in shares)	300,000,000		300,000,000
Ordinary shares, issued (in shares)	57,504,000		58,898,000
Ordinary shares, outstanding (in shares)	57,504,000		58,898,000
Nonvoting Euro Deferred shares, par value (in euros per share) | € / shares		€ 0.01		€ 0.01
Nonvoting Euro Deferred shares, authorized (in shares)	4,000,000		4,000,000
Nonvoting Euro Deferred shares, issued (in shares)	4,000,000		4,000,000
Nonvoting Euro Deferred shares, outstanding (in shares)	4,000,000		4,000,000