Debt (Details)	1 Months Ended	3 Months Ended
	May 31, 2013 USD ($)	Mar. 31, 2017 USD ($) installment	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Principal Payments
Total debt		$ 226,300,000		$ 220,900,000
Deferred financing costs		(3,600,000)		(3,800,000)
Less: Debt payable within one year		1,200,000		1,200,000
Long-term debt		225,100,000		$ 219,700,000
Scheduled debt repayment		300,000	$ 300,000
Repayment of daily cash management activities		5,200,000
Long-term debt borrowings			$ 7,600,000
Global Revolving Credit Facilities (variable rates) due December 2019
Principal Payments
Letters of credit outstanding		1,200,000
Available credit		$ 120,800,000
Weighted-average interest rate (as a percent)		3.10%		2.80%
Senior notes | 2021 Senior Notes (5.25% fixed rate) due May 2021
Principal Payments
Total debt		$ 175,000,000		$ 175,000,000
Debt instrument, interest rate, stated percentage		5.25%
Total term of notes	8 years
Face amount	$ 175,000,000
Line of credit | Global Revolving Credit Facilities (variable rates) due December 2019
Principal Payments
Total debt		$ 48,300,000		42,900,000
Secured debt | German loan agreement (2.45% fixed rate) due in 32 equal quarterly installments ending September 2022
Principal Payments
Total debt		$ 6,600,000		$ 6,800,000
Debt instrument, interest rate, stated percentage		2.45%
Debt instrument, due number of equal quarterly installments | installment		32