Shareholders Equity - Additional Information (Detail)								3 Months Ended		9 Months Ended
	Sep. 17, 2020 USD ($)	Sep. 15, 2020 USD ($)	Sep. 11, 2020 USD ($)	Aug. 07, 2020 $ / shares	Jul. 09, 2020 USD ($) $ / shares Rate shares	Sep. 13, 2019 USD ($)	Aug. 06, 2019 $ / shares	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares	Dec. 31, 2019 $ / shares shares	May 03, 2016 USD ($)
Class of Stock [Line Items]
Dividends declared per common share (in dollars per share)				$ 0.31			$ 0.31	$ 0.31	$ 0.31	$ 0.93	$ 0.93
Cash dividends paid - common shares, total | $			$ 10,900,000			$ 10,900,000		$ 10,900,000	$ 9,800,000	$ 32,200,000	$ 32,500,000
Preferred shares par value (in dollars per share)								$ 1.00		$ 1.00		$ 1.00
Fractional interest per one preference share					0.001
Liquidation preference (in dollars per share)								$ 25,000		$ 25,000
Depositary shares, dividends per share (in dollars per share)				0.330556
Number of shares repurchased (in shares) | shares										0
Preferred shares, shares issued (in shares) | shares								6,000		6,000		0
Depositary shares issued (in shares) | shares					6,000,000
Liquidation preference per depository share (in dollars per share)					$ 25
Proceeds from sale of depositary shares | $					$ 144,000,000
Repayment of debt | $	$ 125,000,000
Preferred dividends, per depositary share amounts (in dollars per share)					$ 1.75
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividends declared (in dollars per share)				330.556
Preferred stock, dividend rate (in percentage)					7.00%
Preferred shares par value (in dollars per share)				1.00
Liquidation preference (in dollars per share)				$ 25,000	$ 25,000
Payments of dividends | $		$ 2,000,000.0
Preferred shares, shares issued (in shares) | shares					6,000
Preferred dividends (in dollars per share)					$ 1,750
Series A Preferred Stock | U.S. Treasury Rate
Class of Stock [Line Items]
Basis spread on U.S. Treasury Rate | Rate					6.712%
2016 Repurchase Authorization
Class of Stock [Line Items]
Total number of shares authorized for purchase | $													$ 150,000,000.0
Remaining number of shares available under repurchase authorization | $								$ 53,300,000		$ 53,300,000