Receivables and Allowance for Doubtful Accounts Receivables and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Receivables [Line Items]
Accounts Receivable, Gross	$ 73,990	$ 73,378
Receivables, net of allowance for doubtful accounts of $4,167 and $3,593 in 2017 and 2016, respectively	69,823	69,785
Changes in allowance for doubtful accounts [Roll Forward]
Bad debt expense	15,702	15,449	$ 15,260
Accounts written off	(15,791)	(16,095)	(16,317)
Recoveries	663	625	648
Allowance for doubtful accounts	(4,167)	(3,593)	$ (3,614)	$ (4,023)
Installment sales receivable [Member]
Receivables [Line Items]
Accounts Receivable, Gross	55,516	55,834
Changes in allowance for doubtful accounts [Roll Forward]
Allowance for doubtful accounts	(3,600)	(3,300)
Trade and notes receivables [Member]
Receivables [Line Items]
Accounts Receivable, Gross	18,474	14,067
Changes in allowance for doubtful accounts [Roll Forward]
Allowance for doubtful accounts	(600)	(300)
Other receivables [Member]
Receivables [Line Items]
Accounts Receivable, Gross	$ 0	$ 3,477