Stockholders' Equity - Additional Information (Detail) - USD ($)			1 Months Ended		3 Months Ended		6 Months Ended
	Mar. 01, 2022	Mar. 01, 2021	Feb. 28, 2021	Mar. 31, 2018	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Shareholders Equity [Line Items]
Payment of regular quarterly dividend							$ 39,085,000	$ 35,022,000
Regular quarterly dividends paid per share							$ 0.82	$ 0.78
Shares issued pursuant to dividend reinvestment, shares							996	1,258
Proceeds from issuance of common stock under the dividend reinvestment plan							$ 30,000	$ 36,000
Stock based compensation expense							$ 2,316,000	$ 1,937,000
Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to dividend reinvestment, shares					1,000		1,000	1,000
2018 ATM Program [Member] | Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to Offering/Program net, shares					0	289,000	0	1,032,000
Proceeds from issuance of common stock, net						$ 9,312,000		$ 29,578,000
2018 ATM Program [Member] | Maximum [Member]
Shareholders Equity [Line Items]
Aggregate sales price				$ 125,000,000
ATM Program [Member]
Shareholders Equity [Line Items]
Proceeds from issuance of common stock, net							$ (83,000)	$ 29,578,000
ATM Program [Member] | Common Stock [Member]
Shareholders Equity [Line Items]
Shares issued pursuant to Offering/Program net, shares						289,000		1,032,000
ATM Program [Member] | Maximum [Member]
Shareholders Equity [Line Items]
Aggregate sales price			$ 250,000,000
Amended and Restated 2004 Omnibus Incentive Compensation Plan [Member] | Restricted Stock Units [Member]
Shareholders Equity [Line Items]
Restricted stock units, granted	238,850	192,550