Current and Long-Term Debt - Components of Debt (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Apr. 04, 2017	Nov. 19, 2013
Long-Term Debt
Total Debt	$ 778,177,000	$ 739,475,000
Less: Current portion	(5,000,000)	0
Long-term debt	773,177,000	739,475,000
Revolving Credit Facility
Long-Term Debt
Total Debt	0	167,227,000
Term Loan Due 2027
Long-Term Debt
Total Debt	480,985,000	0
Aggregate principle amount	497,500,000
Unamortized discount and capitalized debt issuance costs	16,500,000
Debt Instrument, Periodic Payment	5,000,000.0
Senior Notes 5.50 Percent Due 2025
Long-Term Debt
Total Debt	$ 297,192,000	$ 296,545,000
Interest rate	5.50%	5.50%	5.50%
Aggregate principle amount	$ 300,000,000.0		$ 300,000,000.0
Capitalized debt issuance costs	2,800,000	$ 3,500,000
Convertible Notes
Long-Term Debt
Total Debt	$ 0	$ 275,703,000
Interest rate	1.00%	1.00%		1.00%
Aggregate principle amount		$ 287,500,000		$ 287,500,000
Unamortized discount and capitalized debt issuance costs		$ 11,800,000