Receivables Rollforward of Allowance for Doubtful Accounts (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Installment Receivables [Member]	Dec. 31, 2013 Installment Receivables [Member]
Allowance for Doubtful Accounts [Roll Forward]
Balance as of January 1	$ 6,039		$ 6,039	$ 3,823
Current period provision	663	768	322	3,457
Direct write-offs charged against the allowance			(140)	(1,241)
Balance as of December 31	$ 6,221		$ 6,221	$ 6,039