Accounts receivable reserve (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Changes in the reserves against current billed accounts receivable
Contractual retainage provisions	$ 8,300,000	$ 3,200,000
Accounts receivable, billed and unbilled
Changes in the reserves against current billed accounts receivable
Balance at beginning of year	3,975,000	3,265,000	1,845,000
Additions to reserve	2,334,000	2,061,000	3,063,000
Deductions	(2,481,000)	(1,351,000)	(1,643,000)
Balance at end of year	$ 3,828,000	$ 3,975,000	$ 3,265,000