Equity based compensation (Narrative) (Details) (USD $)	0 Months Ended	9 Months Ended	0 Months Ended							0 Months Ended			9 Months Ended	0 Months Ended
	Aug. 14, 2013 Nonvested Stock [Member]	Sep. 30, 2013 Nonvested Stock [Member]	Aug. 14, 2013 Nonvested Stock [Member] Initial Three Year Vesting Period [Member]	Aug. 14, 2013 Nonvested Stock [Member] Year Two Through Four Vesting Period [Member]	Aug. 14, 2013 Stock Option [Member]	Sep. 30, 2013 Stock Option [Member]	Dec. 31, 2012 Stock Option [Member]	Aug. 14, 2013 Stock Option [Member] $6.92 [Member]	Aug. 14, 2013 Stock Option [Member] $7.10 [Member]	Aug. 14, 2013 Stock Option [Member] Initial Three Year Vesting Period [Member] $6.92 [Member]	Aug. 14, 2013 Stock Option [Member] Year Two Through Four Vesting Period [Member] $7.10 [Member]	Aug. 14, 2013 Restricted Stock Units [Member] director	Sep. 30, 2013 Restricted Stock Units [Member]	Aug. 14, 2013 Restricted Stock Units [Member] One Year Vesting Period [Member]	Aug. 14, 2013 Restricted Stock Units [Member] Two Year Vesting Period [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	42,858	589,102			463,106							10,000	10,000
Number of shares vesting			19,048	23,810						370,604	92,502
Grant date fair value (usd per share)	$ 13.96							$ 6.92	$ 7.10			$ 13.96
Exercise price (usd per share)					$ 14.00	$ 9.72	$ 0.97
Number of directors receiving RSUs												2
Percentage of award vesting														50.00%	50.00%