Receivables and Allowance for Doubtful Accounts Receivables and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Line Items]
Accounts Receivable, Gross	$ 74,528	$ 73,990
Receivables, net of allowance for doubtful accounts of $4,883 and $4,167 in 2018 and 2017, respectively	69,645	69,823
Changes in allowance for doubtful accounts [Roll Forward]
Bad debt expense	14,610	15,702	$ 15,449
Accounts written off	(14,475)	(15,791)	(16,095)
Recoveries	581	663	625
Allowance for doubtful accounts	(4,883)	(4,167)	$ (3,593)	$ (3,614)
Installment sales receivable [Member]
Receivables [Line Items]
Accounts Receivable, Gross	54,746	55,516
Changes in allowance for doubtful accounts [Roll Forward]
Allowance for doubtful accounts	(3,600)	(3,600)
Trade and notes receivables [Member]
Receivables [Line Items]
Accounts Receivable, Gross	19,782	18,474
Changes in allowance for doubtful accounts [Roll Forward]
Allowance for doubtful accounts	$ (1,300)	$ (600)