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Shareholders equity.

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Stockholders' Equity - Additional Information (Detail) - USD ($)				1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 31, 2025	Mar. 01, 2024	Mar. 01, 2023	Jul. 31, 2024	Feb. 28, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Shareholders Equity [Line Items]
Payment of regular quarterly dividend								$ 74,800,000	$ 63,800,000
Regular quarterly dividends paid per share								$ 1.35	$ 1.29
Shares issued pursuant to dividend reinvestment, shares								1,643	1,178
Shares issued pursuant to dividend reinvestment, value						$ 16,000	$ 12,000	$ 46,000	$ 40,000
Proceeds from issuance of common stock under the dividend reinvestment plan								46,000	40,000
Stock based compensation expense								$ 4,500,000	$ 4,200,000
Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to Offering/Program net, shares							2,200,000		2,200,000
Shares issued pursuant to dividend reinvestment, shares						1,000	1,000	1,000	1,000
July 2024 Forward Offering [Member]
Shareholders Equity [Line Items]
Number of shares settled under forward provisions						0		0
July 2024 Forward Offering [Member] \| Scenario Forecast [Member]
Shareholders Equity [Line Items]
Proceeds from issuance of common stock, net	$ 121,100,000
February 2023 Forward Offering [Member]
Shareholders Equity [Line Items]
Proceeds from issuance of common stock, net							$ 71,500,000			$ 112,100,000
Number of shares settled under forward provisions							2,200,000			3,500,000
Follow-on Public Offering [Member] \| July 2024 Forward Offering [Member] \| Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to Offering/Program net, shares				4,000,000
Follow-on Public Offering [Member] \| February 2023 Forward Offering [Member] \| Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to Offering/Program net, shares					3,500,000
ATM Program [Member]
Shareholders Equity [Line Items]
Proceeds from issuance of common stock, net						$ 23,900,000		$ 31,100,000	$ 114,100,000
Number of shares allowed for sale under forward provisions								400,000	200,000
Sale of common stock average gross offering price per share						$ 27.98	$ 34.97	$ 27.98	$ 34.97
Number of shares settled under forward provisions						800,000		1,000,000	3,700,000
ATM Program [Member] \| Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to Offering/Program net, shares						831,000		1,049,000	3,721,000
Number of shares allowed for sale under forward provisions								400,000
ATM Program [Member] \| Maximum [Member]
Shareholders Equity [Line Items]
Aggregate sales price					$ 350,000,000
ATM Direct Issuances [Member] \| Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to Offering/Program net, shares						0	0	0	0
Amended and Restated 2004 Omnibus Incentive Compensation Plan [Member] \| Restricted Stock Units [Member]
Shareholders Equity [Line Items]
Granted, Number of RSUs Outstanding		271,250	253,075