Dividends and Equity Issuance Program - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Dividends and Equity Issuance [Line Items]
Dividends declared	$ 9,501		$ 9,355	$ 28,426	$ 27,988
Declared dividends, per share	$ 0.69			$ 2.065
Dividends payable, date to be paid	Sep. 30, 2020
Dividends declared and paid	$ 9,500		$ 9,400	$ 28,411	$ 27,988
Declared and paid dividends, per share	$ 0.69		$ 0.68	$ 2.065	$ 2.035
At-The-Market Equity Issuance Program (ATM)
Dividends and Equity Issuance [Line Items]
Aggregate sales of threshold amount		$ 100,000
Issued (in shares)	0	2,704
Average sale price per share		$ 101.30
Net cash proceeds from stock issued		$ 270,000
Payment 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				$ 507,000