Stockholders' equity (Details 3) (USD $)	Dec. 31, 2013	Sep. 30, 2013
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	9,544,657	9,559,113
Second Quarter Current Year [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	35,380
Weighted Average Exercise Price	$ 8.70
Third Quarter Current Year [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	57,333
Weighted Average Exercise Price	$ 9.75
Fourth Quarter Current Year [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	35,000
Weighted Average Exercise Price	$ 7.64
First Quarter Year One [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	81,973
Weighted Average Exercise Price	$ 7.80
Second Quarter Year One [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	78,100
Weighted Average Exercise Price	$ 7.80
Third Quarter Year One [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	10,600
Weighted Average Exercise Price	$ 10.05
Fourth Quarter Year One [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	83,918
Weighted Average Exercise Price	$ 6.60
First Quarter Year Two [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	479,246
Weighted Average Exercise Price	$ 7.65
Second Quarter Year Two [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	872,800
Weighted Average Exercise Price	$ 7.20
Third Quarter Year Two [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	960,100
Weighted Average Exercise Price	$ 6.45
Fourth Quarter Year Two [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	1,263,958
Weighted Average Exercise Price	$ 6.90
First Quarter Year Three [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	516,808
Weighted Average Exercise Price	$ 7.80
Second Quarter Year Three [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	859,750
Weighted Average Exercise Price	$ 6.15
Third Quarter Year Three [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	1,076,475
Weighted Average Exercise Price	$ 7.65
Fourth Quarter Year Three [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	1,599,208
Weighted Average Exercise Price	$ 6.75
First Quarter Year Four [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	1,195,675
Weighted Average Exercise Price	$ 6.75
Second Quarter Year Four [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	66,667
Weighted Average Exercise Price	$ 5.85
First Quarter Year Five [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	138,333
Weighted Average Exercise Price	$ 1.95
First Quarter Year Nine [Member]
Share Based Payment Award, By Expiration Fiscal Period [Line Items]
Outstanding	133,333
Weighted Average Exercise Price	$ 7.05