Condensed Consolidated Balance Sheets (Parenthetical) $ in Thousands	Mar. 31, 2020 € / shares	Mar. 31, 2020 USD ($) shares	Dec. 31, 2019 € / shares	Dec. 31, 2019 USD ($) shares
Current assets:
Accounts receivable, allowances | $		$ 15,832		$ 15,129
Accumulated amortization | $		$ 2,072,227		$ 2,039,436
Shareholders’ equity:
Ordinary shares, nominal value per share (in euros per share) | € / shares	€ 0.01		€ 0.01
Common stock, shares authorized (in shares)		177,069,000		177,069,000
Common stock, shares, issued (in shares)		172,596,000		172,561,000
Treasury stock, shares (in shares)		15,631,000		14,733,000