Stock incentive plan (Details 2) - Restricted Stock [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016
Schedule Of Nonvested Restricted Stock Units Activity [Line Items]
Begining Balance			47,893
Shares, Granted	6,250	40,675	10,850
Shares, Vested			(16,264)
Shares, Forfeited			(3,399)
Ending Balance			39,080
Weighted-Average Grant-Date Fair-Value, Begining Balance			$ 21.04
Weighted-Average Grant-Date Fair-Value, Granted	$ 22.50	$ 19.72	21.88
Weighted-Average Grant-Date Fair-Value, Vested			20.85
Weighted-Average Grant-Date Fair-Value, Forfeited			(21.53)
Weighted-Average Grant-Date Fair-Value, Ending Balance			$ 20.82
Aggregate Intrinsic Value, Begining Balance			$ 1,043,444
Aggregate Intrinsic Value, Granted			289,695
Aggregate Intrinsic Value, Vested			(434,257)
Aggregate Intrinsic Value, Forfeited			(90,727)
Aggregate Intrinsic Value, Ending Balance			$ 1,278,733