Debt with Commercial Bank (Narrative) (Details)			3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 17, 2016 USD ($) Companies	Aug. 05, 2014	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Oct. 14, 2015 USD ($)
Line of Credit Facility [Line Items]
Proceeds from Lines of Credit				$ 80,000,000
Deferred Costs, Current			$ 136,000	136,000	$ 136,000	$ 136,000
Deferred Costs, Noncurrent			367,000	367,000	367,000	$ 452,000
Secured Syndicated Credit Facility, Second Amendment [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 400,000,000
Credit agreement, maximum borrowing capacity	$ 500,000,000
Number of Participating Banks | Companies	11
Newly Added Number of Participating Banks | Companies	7
Deferred Costs, Credit Card Origination Costs, Amount			2,660,000	2,660,000	2,660,000
Secured Syndicated Credit Facility, Second Amendment [Member] | Secured Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 125,000,000
Line of Credit Facility, Term	5 years
Debt Instrument, Periodic Payment, Principal				9,000,000
Loans Payable			109,400,000	109,400,000	109,400,000
Loans Payable, Current			12,500,000	12,500,000	$ 12,500,000
Line of Credit Facility, Short Term					12 months
Line of Credit Facility, Periodic Payment, Principal			3,130,000
Short-term Debt			12,500,000	12,500,000	$ 12,500,000
Long-term Debt, Gross			96,900,000	96,900,000	96,900,000
Deferred Costs, Credit Card Origination Costs, Amount			$ 503,000	$ 503,000	$ 503,000
Line of credit, interest rate at period end			4.00%	4.00%	4.00%
Deferred Costs, Current			$ 136,000	$ 136,000	$ 136,000
Deferred Costs, Noncurrent			367,000	367,000	367,000
Secured Syndicated Credit Facility, Second Amendment [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 275,000,000
Line of Credit Facility, Term	5 years
Deferred Costs, Credit Card Origination Costs, Amount			$ 2,160,000	$ 2,160,000	$ 2,160,000
Line of credit, interest rate at period end			4.00%	4.00%	4.00%
Secured Syndicated Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Debt Instrument, 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			$ 234,029,000	$ 234,029,000	$ 234,029,000
Secured Syndicated Credit Facility [Member] | Revolving Credit Facility [Member] | Citi Bank [Member]
Line of Credit Facility [Line Items]
Credit agreement, average amount outstanding during period				191,500,000
Credit agreement, maximum amount outstanding during period				$ 234,000,000
Secured Syndicated Credit Facility, First Amendment [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Credit agreement, maximum borrowing capacity							$ 240,000,000