Stock-based expense (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stock-based expense
Number of stock-based compensation programs				2
Stock-based expense
Total stock-based expense	$ 315,968		$ 284,071	$ 864,924	$ 824,468
Stock options
Stock-based expense
Options granted (in shares)		0.9
Fair value of options granted		1,000,000
Requisite service period				36 months
Total stock-based expense	228,423		284,071	739,992	824,468
Restricted stock awards
Stock-based expense
Stock granted (in shares)		0.7
Fair value of awards granted	1,900,000
Total stock-based expense	87,545			124,932
Restricted stock awards | Minimum
Stock-based expense
Requisite service period				12 months
Restricted stock awards | Maximum
Stock-based expense
Requisite service period				36 months
Processing and service costs
Stock-based expense
Total stock-based expense	65,284		67,811	173,089	196,812
Selling, general and administrative expenses
Stock-based expense
Total stock-based expense	$ 250,684		$ 216,260	$ 691,835	$ 627,656