Shareholders' Equity And Earnings Per Share (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended					3 Months Ended		9 Months Ended
	Apr. 27, 2017	Apr. 25, 2017	Dec. 19, 2008	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Jun. 30, 2015	Mar. 31, 2012	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Temporary Equity [Line Items]
Cash dividends declared per common share (usd per share)				$ 0.19	$ 0.19	$ 0.19			$ 0.19	$ 0.14	$ 0.57	$ 0.42
Common stock dividends per share declared annualized (usd per share)				$ 0.76	$ 0.76	$ 0.76
US Treasury
Temporary Equity [Line Items]
Warrants outstanding, shares			1,643,295						7,410		7,410
Warrant termination period			10 years
Investment warrants, exercise price (usd per share)											$ 22.57
Warrants exercised, shares											15,951
Common stock shares issued from exercise of warrants											11,764
Common stock
Temporary Equity [Line Items]
Common stock issued, conversion of preferred stock, shares	3,069,828	51,244
Series D Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares issued (in shares)							5,000,000		5,000,000	5,000,000	5,000,000	5,000,000	5,000,000
Preferred stock, liquidation value per share (usd per share)							$ 25		$ 25	$ 25	$ 25	$ 25	$ 25
Preferred stock, value							$ 125,000		$ 125,000	$ 125,000	$ 125,000	$ 125,000	$ 125,000
Preferred stock, dividend rate, percentage							6.50%
Series C Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares issued (in shares)								126,500
Preferred stock, liquidation value per share (usd per share)								$ 1,000
Preferred stock, value								$ 126,500
Preferred stock, dividend rate, percentage								5.00%
Number of shares converted	124,184	2,073
Convertible preferred stock, rate of conversion, shares	24.72
London Interbank Offered Rate (LIBOR) | Series D Preferred Stock
Temporary Equity [Line Items]
Preferred stock, dividend rate, percentage, variable spread							4.06%