Shareholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares	Jul. 09, 2020 $ / shares	May 03, 2016 USD ($)
Class of Stock [Line Items]
Preferred shares, issued (in shares) | shares	6,000	6,000
Depositary shares issued (in shares) | shares	6,000,000
Preferred stock, liquidation preference (in dollars per share)	$ 25,000	$ 25,000
Depositary share, liquidation preference (in dollars per share)	25			$ 25
Preferred stock, per depositary share amounts of preferred dividends (in dollars per share)	$ 1.75
Preferred shares, authorized (in shares) | shares	30,000,000	30,000,000
Preferred shares, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred shares, outstanding (in shares) | shares	6,000	6,000
Dividend declared per common share (in dollars per share)	$ 1.24	$ 1.24	$ 1.24
Cash dividends paid to common stockholders | $	$ 43.9	$ 43.0	$ 43.1
Common shares repurchased on open market (in shares) | shares	0	0
Fractional interest per preference share	0.001
Series A Preferred Stock
Class of Stock [Line Items]
Preferred shares, issued (in shares) | shares	6,000
Preferred stock, liquidation preference (in dollars per share)	$ 25,000			$ 25,000
Dividends declared per preferred share (in dollars per share)	0.0700
Preferred stock dividends (in dollars per share)	$ 1,750
Payments of dividends | $	$ 10.5
Preferred shares, outstanding (in shares) | shares	6,000
Series A Preferred Stock | US Treasury (UST) Interest Rate
Class of Stock [Line Items]
Preferred stock, dividend payment rate, Basis spread on variable rate (in percentage)	0.06712
2016 Repurchase Authorization
Class of Stock [Line Items]
Remaining number of shares available under repurchase authorization, value | $	$ 53.3
Maximum | 2016 Repurchase Authorization
Class of Stock [Line Items]
Total number of shares authorized for purchase, value | $					$ 150.0