Debt - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended
	May 31, 2013	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Principal Payments
Total debt		$ 271,900,000		$ 200,800,000
Net long-term debt borrowings		71,700,000
Net borrowings related to daily cash management		6,700,000
Net borrowings related to increased cash on hand		65,000,000.0
Repayments of debt			$ 7,700,000
Scheduled debt repayment			$ 300,000
Global Revolving Credit Facilities (variable rates)
Principal Payments
Letters of credit outstanding		500,000
Available credit		$ 117,200,000
Weighted-average interest rate (as a percent)		2.40%		1.30%
Senior notes | 2021 Senior Notes (5.25% fixed rate)
Principal Payments
Total term of notes	8 years
Face amount	$ 175,000,000
Maximum number of days after acquisition acquired assets included in domestic borrowing base		60 days
Maximum number of days following acquisition thresholds restricted to redeem senior notes		90 days
Fixed rate of interest		5.25%
Total debt		$ 175,000,000.0		$ 175,000,000.0
Line of credit | Global Revolving Credit Facilities (variable rates)
Principal Payments
Total debt		$ 93,000,000.0		$ 21,600,000