Dividends and Equity Issuance Program - Additional Information (Detail) - USD ($)	12 Months Ended			18 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021	Jun. 30, 2020
Dividends and Equity Issuance [Line Items]
Declared and paid dividends, per share	$ 2.80	$ 2.76	$ 2.72
Ordinary income per share	2.51	2.43	2.48
Capital gain per share	$ 0.16	$ 0.33	$ 0.24
At-The-Market Equity Issuance Program (ATM)
Dividends and Equity Issuance [Line Items]
Aggregate sales of threshold amount					$ 100,000,000
Share issued	0			2,704
Average sale price per share	$ 101.30
Net cash proceeds from stock issued	$ 270,000
Payments of stock issuance cost	4,000
At-The-Market Equity Issuance Program (ATM) | Other Expenses
Dividends and Equity Issuance [Line Items]
Payments for stock issuance	$ 508,000
Capital gain
Dividends and Equity Issuance [Line Items]
Capital gain per share	$ 0.13
Unrecaptured Section 1250 gain dividends per share	$ 0.04