Consolidated Balance Sheets Balance Sheet Parenthetical $ in Thousands	Mar. 31, 2018 € / shares	Mar. 31, 2018 USD ($) shares	Dec. 31, 2017 € / shares	Dec. 31, 2017 USD ($) shares
Allowance for doubtful accounts | $		$ 2,644		$ 2,590
Common stock, par value (euro per share) | € / shares	€ 0.02		€ 0.02
Common stock, shares authorized (in shares)		200,000,000		200,000,000
Common stock, shares issued (in shares)		44,796,252.000		44,796,252
Common stock, shares outstanding (in shares)		44,189,593.000		44,184,205
Treasury Stock (euro per share)		606,659.000		612,047
Preferred stock, par value (in shares) | € / shares	€ 0.02		€ 0.02
Preferred stock, shares authorized (in shares)		6,000,000		6,000,000
Preferred stock, shares issued (in shares)		0		0
Preferred stock, shares outstanding (in shares)		0		0