Consolidated Balance Sheets Balance Sheet Parenthetical $ in Thousands	Sep. 30, 2018 € / shares	Sep. 30, 2018 USD ($) shares	Dec. 31, 2017 € / shares	Dec. 31, 2017 USD ($) shares
Statement of Financial Position [Abstract]
Allowance for doubtful accounts | $		$ 2,841		$ 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		44,796,252
Common stock, shares outstanding (in shares)		44,220,731		44,184,205
Treasury stock (in share)		575,521		612,047
Preferred stock, par value (euro per share) | € / 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