Summary of significant accounting policies (Details 6) (USD $)	12 Months Ended			1 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended		12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Mar. 31, 2011	Jul. 31, 2011 Restricted stock with performance goals CEO	Dec. 31, 2012 Restricted stock with performance goals CEO item	Jul. 31, 2011 Restricted stock with performance conditions	Jul. 31, 2011 Restricted stock with performance conditions, tranche 1	Dec. 31, 2012 Restricted stock with performance conditions, tranche 1 Minimum	Jul. 31, 2011 Restricted stock with performance conditions, tranche 2	Dec. 31, 2012 Restricted stock with performance conditions, tranche 2 Minimum	Jul. 31, 2011 Restricted stock with performance conditions, tranche 3	Dec. 31, 2012 Restricted stock with performance conditions, tranche 3 Minimum	Jul. 31, 2011 Restricted stock with market conditions	Jul. 31, 2011 Restricted stock with market conditions, tranche 4	Dec. 31, 2012 Restricted stock with market conditions, tranche 4 item	Dec. 31, 2012 Restricted stock with market conditions, tranche 4 Minimum
Long-term incentive restricted stock agreement assumptions and vesting requirements
Stock granted (in shares)				915,000			305,000		47,000		469,000			94,000
Number of separate tranches in which stock-based award will vest					4
Adjusted EBITDA per fully diluted share when upon achievement shares will vest (in dollars per share)								$ 0.36		$ 0.64		$ 0.71
Fair value						$ 1,800,000	$ 700,000		$ 100,000		$ 1,000,000		$ 5,600	$ 5,600
Fair market value of stock upon achievement of which share will be vested (in dollars per share)																$ 12.00
Number of consecutive trading days during which the fair market value of the entity's common stock must exceed the specified price in order for the award to vest															75
Valuation assumptions used for estimated fair value on grant date
Expected life													5 years 3 months 18 days
Expected volatility (percentage)													31.68%
Risk-free interest rate (percentage)													2.04%
Notes payable derecognition amount on which statute of limitations expired		40,000	660,000
Derecognition of note payable	700,000
Other income recorded due to derecognition of note payable	$ 700,000