Series A redeemable convertible preferred stock (Details) (Series A Preferred Stock, USD $)	1 Months Ended		3 Months Ended	12 Months Ended
	Apr. 30, 2014	Feb. 28, 2014	Mar. 31, 2015 installment item	Dec. 31, 2013	Dec. 31, 2014
Series A Preferred Stock
Class of Stock
Preferred stock, shares issued	594,904	1,405,096		1,999,864
Share value (in dollars per share)				$ 1.00
Senior notes converted into shares				$ 1,999,864
Proceeds from issuance of convertible preferred stock	$ 594,904	$ 1,405,096
Preferred stock, shares outstanding			3,999,864		3,999,864
Number of shares of common stock into which the outstanding preferred stock can be converted			3,999,864		3,999,864
Dividend rate (as a percent)			8.00%
Liquidation and redemption preference, multiple of the purchase price			2
Number of shares issued upon conversion of stock			1
Request of minimum holders' of outstanding preferred stock required for redemption (as a percent)			70
Number of installments in redemption			3
Redemption price expressed as a multiple of the original price of preferred stock plus all accrued and unpaid dividends			2