Summary of Significant Accounting Policies - Reserve for Transaction Losses (Details) (Reserve For Transaction Losses [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reserve For Transaction Losses [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 223	$ 547	$ 774
Additions to expense	13,346	13,579	7,722
Losses incurred, net of recoveries	(13,380)	(13,903)	(7,949)
Balance at End of Year	$ 189	$ 223	$ 547