Debt with Commercial Bank (Narrative) (Details)				3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 21, 2018 USD ($) Companies	Jun. 17, 2016	Aug. 05, 2014	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019	Sep. 30, 2019 USD ($)	Nov. 27, 2018 USD ($)	Apr. 09, 2018 USD ($)
Line of Credit Facility [Line Items]
Proceeds from Lines of Credit						$ 13,500,000
Deferred Costs, Current				$ 575,000	$ 575,000	575,000			$ 575,000
Deferred Costs, Noncurrent				$ 1,703,000	1,811,000	$ 1,703,000			$ 1,703,000
Secured Syndicated Credit Facility, Eighth Amendment [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Deferred Costs, Credit Card Origination Costs, Amount					5,900,000
Secured Syndicated Credit Facility, Eighth Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity										$ 301,250,000
Loans Payable					291,200,000
Loans Payable, Current					15,100,000
Line of Credit Facility, Short Term								12 months
Line of Credit Facility, Periodic Payment, Principal					3,770,000
Short-term Debt					15,100,000
Long-term Debt, Gross					276,200,000
Deferred Costs, Credit Card Origination Costs, Amount					2,400,000
Deferred Costs, Current					575,000
Deferred Costs, Noncurrent					1,800,000
Secured Syndicated Credit Facility, Eighth Amendment [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity										450,000,000
Deferred Costs, Credit Card Origination Costs, Amount					$ 3,500,000
Line of credit, interest rate at period end				4.80%	4.88%	4.80%			4.80%
Credit agreement, average amount outstanding during period							$ 318,900,000
Credit agreement, maximum amount outstanding during period							$ 424,500,000
Secured Syndicated Credit Facility, Seventh Amendment [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Permitted indebtedness in the form of unsecured convertible notes											$ 300,000,000
Secured Syndicated Credit Facility, Fifth Amendment [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Credit agreement, maximum borrowing capacity	$ 450,000,000
Secured Syndicated Credit Facility, Sixth Amendment [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Permitted indebtedness in the form of unsecured convertible notes	250,000,000
Line of Credit Facility, Current Borrowing Capacity	$ 650,000,000
Debt Instrument, Term			5 years
Number of Participating Banks | Companies	10
Secured Syndicated Credit Facility, Sixth Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 250,000,000
Line of Credit Facility, Term	5 years
Line of Credit Facility, Periodic Payment, Principal				$ 3,130,000
Secured Syndicated Credit Facility, Sixth Amendment [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
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, Ninth Amendment [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Deferred Costs, Credit Card Origination Costs, Amount				5,700,000		$ 5,700,000			$ 5,700,000
Secured Syndicated Credit Facility, Ninth Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Periodic Payment, Principal						11,300,000
Loans Payable				279,900,000		279,900,000			279,900,000
Loans Payable, Current				18,800,000		18,800,000			$ 18,800,000
Line of Credit Facility, Short Term									12 months
Short-term Debt				18,800,000		18,800,000			$ 18,800,000
Long-term Debt, Gross				261,100,000		261,100,000			261,100,000
Deferred Costs, Credit Card Origination Costs, Amount				2,300,000		2,300,000			2,300,000
Deferred Costs, Current				575,000		575,000			575,000
Deferred Costs, Noncurrent				1,700,000		1,700,000			1,700,000
Secured Syndicated Credit Facility, Ninth Amendment [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Deferred Costs, Credit Card Origination Costs, Amount				$ 3,400,000		$ 3,400,000			$ 3,400,000
Line of credit, interest rate at period end				4.81%		4.81%			4.81%
Credit agreement, average amount outstanding during period						$ 436,900,000
Credit agreement, maximum amount outstanding during period						438,000,000.0
Secured Syndicated Credit Facility, Second Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Term		5 years
Secured Syndicated Credit Facility, Second Amendment [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Term		5 years
Secured Syndicated Credit Facility [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Credit agreement, amount outstanding				$ 438,000,000.0	$ 424,500,000	$ 438,000,000.0			$ 438,000,000.0
Minimum [Member] | Secured Syndicated Credit Facility, Eighth Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit, Accordion										101,250,000
Maximum [Member] | Secured Syndicated Credit Facility, Eighth Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit, Accordion										$ 150,000,000
Maximum [Member] | Secured Syndicated Credit Facility, Sixth Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit, Accordion	$ 150,000,000