Receivables and Allowance for Doubtful Accounts Receivables and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Receivables [Line Items]
Accounts Receivable, Gross	$ 68,660		$ 73,990
Receivables, net of allowance for doubtful accounts of $3,837 and $4,167 in 2018 and 2017, respectively	64,823		69,823
Allowance for Doubtful Accounts Receivable [Roll Forward]
Bad debt expense	3,437	$ 3,422	15,702
Accounts written off	(3,958)		(15,791)
Recoveries	191		663
Allowance for doubtful accounts	3,837		4,167	$ 3,593
Installment sales receivable [Member]
Receivables [Line Items]
Accounts Receivable, Gross	52,615		55,516
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts	3,200		3,600
Trade and notes receivables [Member]
Receivables [Line Items]
Accounts Receivable, Gross	16,045		18,474
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts	600		600
Other receivables [Member]
Receivables [Line Items]
Accounts Receivable, Gross	$ 0		$ 0