Net income (loss) per common share - Additional Information (Detail)				3 Months Ended		9 Months Ended	12 Months Ended	3 Months Ended
	Sep. 30, 2014 Restricted Stock Units RSU Member Management Member	Dec. 31, 2013 Restricted Stock Units RSU Member Management Member	Dec. 31, 2012 Restricted Stock Units RSU Member Management Member	Sep. 30, 2014 Employee Stock Option[Member]	Sep. 30, 2013 Employee Stock Option[Member]	Sep. 30, 2014 Employee Stock Option[Member]	Dec. 31, 2013 Employee Stock Option[Member]	Sep. 30, 2014 Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount				44,797	101,755	45,343	103,047	2,093,284
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	510,449	585,247	491,223