Commercial Bank Financing Facility (Details)		3 Months Ended	6 Months Ended	12 Months Ended
	Feb. 21, 2018 USD ($) Companies	Dec. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Nov. 27, 2018 USD ($)	Apr. 09, 2018 USD ($)
Secured Syndicated Credit Facility, Eighth Amendment | Revolving Credit Facility | Regions Bank
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity						$ 450,000,000
Secured Syndicated Credit Facility, Eighth Amendment | Secured Term Loan | Regions Bank
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity						301,250,000
Line of credit facility, periodic payment, principal		$ 3,770,000
Secured Syndicated Credit Facility, Fifth Amendment | Revolving Credit Facility | Regions Bank
Line of Credit Facility [Line Items]
Credit agreement, maximum borrowing capacity	$ 450,000,000
Secured Syndicated Credit Facility | Revolving Credit Facility | Citi Bank
Line of Credit Facility [Line Items]
Credit agreement, amount outstanding		$ 438,000,000.0		$ 438,000,000.0	$ 424,500,000
Line of credit, interest rate at period end		4.25%		4.25%
Credit agreement, average amount outstanding during period				$ 437,200,000
Credit agreement, maximum amount outstanding during period				$ 438,000,000.0
Weighted average interest rate		4.90%		4.90%	4.88%
Secured Syndicated Credit Facility, Second Amendment | Secured Term Loan | Regions Bank
Line of Credit Facility [Line Items]
Loans payable		$ 276,200,000		$ 276,200,000
Loans payable, current		20,700,000		20,700,000
Short-term debt		20,700,000		20,700,000
Long-term debt, gross		$ 255,500,000		$ 255,500,000
Secured Syndicated Credit Facility, Sixth Amendment | Regions Bank
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 650,000,000
Number of participating banks | Companies	10
Permitted indebtedness in the form of unsecured convertible notes	$ 250,000,000
Secured Syndicated Credit Facility, Sixth Amendment | Revolving Credit Facility | Regions Bank
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 400,000,000
Line of credit facility, term	5 years
Secured Syndicated Credit Facility, Sixth Amendment | Secured Term Loan | Regions Bank
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 250,000,000
Line of credit facility, periodic payment, principal			$ 3,130,000
Line of credit facility, term	5 years
Secured Syndicated Credit Facility, Seventh Amendment | Regions Bank
Line of Credit Facility [Line Items]
Permitted indebtedness in the form of unsecured convertible notes							$ 300,000,000
Minimum | Secured Syndicated Credit Facility, Eighth Amendment | Secured Term Loan | Regions Bank
Line of Credit Facility [Line Items]
Line of credit, accordion						101,250,000
Maximum | Secured Syndicated Credit Facility, Eighth Amendment | Secured Term Loan | Regions Bank
Line of Credit Facility [Line Items]
Line of credit, accordion						$ 150,000,000
Maximum | Secured Syndicated Credit Facility, Sixth Amendment | Secured Term Loan | Regions Bank
Line of Credit Facility [Line Items]
Line of credit, accordion	$ 150,000,000