CONDENSED CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDER'S EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Common Stock Outstanding	Paid-in Capital	Retained Earnings	AOCI	Laclede Gas	Laclede Gas Common Stock Outstanding	Laclede Gas Paid-in Capital	Laclede Gas Retained Earnings	Laclede Gas AOCI	Alagasco	Alagasco Common Stock Outstanding	Alagasco Paid-in Capital	Alagasco Retained Earnings
Beginning Balance at Sep. 30, 2015	$ 1,573.6	$ 43.3	$ 1,038.1	$ 494.2	$ (2.0)	$ 1,037.8	$ 0.1	$ 748.2	$ 291.2	$ (1.7)	$ 874.6	$ 0.0	$ 480.9	$ 393.7
Beginning Balance, (in shares) at Sep. 30, 2015		43,335,012					24,577					1,972,052
Stockholders' Equity Rollforward
Net income	46.9			46.9		39.4			39.4		9.9			9.9
Dividend reinvestment plan	0.3		0.3
Dividend reinvestment plan (in shares)		5,866
Stock-based compensation costs	1.7		1.7			1.2		1.2
Stock issued under stock-based compensation plans	0.3	$ 0.1	0.2
Stock issued under stock-based compensation plans (in shares)		106,306
Employee’s tax withholding for stock-based compensation	(1.6)		(1.6)
Employee's tax withholding for stock-based compensation (in shares)		(29,083)
Return of capital to Spire											(9.0)		(9.0)
Dividends declared	(21.2)			(21.2)		(21.2)			(21.2)		(7.5)			(7.5)
Other comprehensive income (loss), net of tax	0.3				0.3	0.1				0.1
Ending Balance at Dec. 31, 2015	1,600.3	$ 43.4	1,038.7	519.9	(1.7)	1,057.3	$ 0.1	749.4	309.4	(1.6)	868.0	$ 0.0	471.9	396.1
Ending Balance, (in shares) at Dec. 31, 2015		43,418,101					24,577					1,972,052
Beginning Balance at Sep. 30, 2016	1,768.2	$ 45.6	1,175.9	550.9	(4.2)	1,068.5	$ 0.1	751.9	318.3	(1.8)	867.3	$ 0.0	451.9	415.4
Beginning Balance, (in shares) at Sep. 30, 2016		45,650,642					24,577					1,972,052
Stockholders' Equity Rollforward
Net income	45.2			45.2		38.0			38.0		10.3			10.3
Dividend reinvestment plan	0.3		0.3
Dividend reinvestment plan (in shares)		5,610
Stock-based compensation costs	1.7		1.7			1.1		1.1
Stock issued under stock-based compensation plans	0.0	$ 0.1	(0.1)
Stock issued under stock-based compensation plans (in shares)		110,136
Employee’s tax withholding for stock-based compensation	(2.1)		(2.1)
Employee's tax withholding for stock-based compensation (in shares)		(33,615)
Dividends declared	(24.0)			(24.0)		(14.7)			(14.7)		(6.7)			(6.7)
Other comprehensive income (loss), net of tax	7.4				7.4	0.2				0.2
Ending Balance at Dec. 31, 2016	$ 1,796.7	$ 45.7	$ 1,175.7	$ 572.1	$ 3.2	$ 1,093.1	$ 0.1	$ 753.0	$ 341.6	$ (1.6)	$ 870.9	$ 0.0	$ 451.9	$ 419.0
Ending Balance, (in shares) at Dec. 31, 2016		45,732,773					24,577					1,972,052