Shareholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Feb. 25, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Cash dividends received	$ 8,367,000		$ 12,694,000	$ 16,139,000	$ 39,448,000
Repurchase of common stock	$ 2,551,000		$ 8,009,000	2,561,000	25,304,000
Market value of shares repurchased under equity compensation plans				$ 451,000	$ 494,000
Employee Stock
Class of Stock [Line Items]
Company's common stock in lieu of cash to exercise options to purchase shares (in shares)	0		0	0	4,668
Other Share Based Awards
Class of Stock [Line Items]
Company's common stock in lieu of cash to exercise options to purchase shares (in shares)	9,660		11,306	9,730	11,439
2021 Stock Repurchase Plan
Class of Stock [Line Items]
Repurchase of common stock (in shares)						2,000,000
Stock repurchase program, percentage of common stock						6.70%
Repurchase of common stock (in shares)	45,354			45,354
Repurchase of common stock	$ 2,101,000			$ 2,101,000
2019 Stock Repurchase Plan
Class of Stock [Line Items]
Repurchase of common stock (in shares)		223
Repurchase of common stock		$ 8,000
Cumulative number of shares repurchased (in shares)							858,717
Common Stock
Class of Stock [Line Items]
Repurchase of common stock (in shares)	55,014		271,299	55,307	829,969
Repurchase of common stock	$ 983,000		$ 4,833,000	$ 988,000	$ 14,795,000
Market value of shares repurchased under equity compensation plans	$ 450,000		$ 346,000	$ 452,000	$ 494,000