Debt - Narrative (Details) - USD ($)	1 Months Ended	9 Months Ended
	May 31, 2013	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Principal Payments
Total debt		$ 204,600,000		$ 239,100,000
Scheduled debt repayment		1,600,000	$ 1,000,000.0
Repayments of debt		31,700,000	$ 3,800,000
Global Revolving Credit Facilities (variable rates)
Principal Payments
Letters of credit outstanding		500,000
Available credit		$ 176,300,000
Weighted-average interest rate (as a percent)		1.30%		2.90%
Senior notes | 2021 Senior Notes (5.25% fixed rate)
Principal Payments
Total term of notes	8 years
Face amount	$ 175,000,000
Total debt		$ 175,000,000.0		$ 175,000,000.0
Line of credit | Global Revolving Credit Facilities (variable rates)
Principal Payments
Total debt		$ 25,100,000		$ 57,900,000