Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Statement of Financial Position [Abstract]
Cash and cash equivalents	$ 53,577	$ 18,934
Accounts receivable	213,016	186,279
Retainage	40,878	29,214
Inventories	24,889	21,543
Costs and estimated earnings in excess of billings	29,937	29,860
Prepaid expenses and other current assets	9,153	10,625
Total current assets	371,450	296,455
Property and equipment, net	24,589	25,746
Goodwill	53,763	50,622
Intangible assets, net	39,357	26,623
Deferred tax assets	33,803	40,874
Operating right of use assets	31,786	0
Other non-current assets	5,780	4,938
Total assets	560,528	445,258
Accounts payable and accrued expenses	186,710	152,909
Billings in excess of costs and estimated earnings	55,739	40,563
Total current liabilities	242,449	193,472
Long-term debt	217	299
Operating long-term lease liabilities	20,530	0
Other non-current liabilities	12,215	1,945
Total liabilities	275,411	195,716
Noncontrolling interest	$ 1,804	$ 3,294
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	10,000,000	10,000,000
Preferred stock, value	$ 0	$ 0
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	22,049,529	22,049,529
Common Stock, Shares, Outstanding	20,762,395	21,165,011
Common stock, value	$ 220	$ 220
Treasury Stock, Shares	1,287,134	884,518
Treasury stock, value	$ (24,499)	$ (12,483)
Additional paid-in capital	200,587	192,911
Retained earnings	107,005	65,600
Total stockholders' equity	283,313	246,248
Total liabilities and stockholders' equity	$ 560,528	$ 445,258
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent