Shareholders' Equity And Earnings Per Share (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended			3 Months Ended				9 Months Ended		12 Months Ended
	Apr. 27, 2017	Apr. 25, 2017	Dec. 19, 2008	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2012	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Temporary Equity [Line Items]
Stock issued in public offering, shares				3,000,000
Proceeds from the issuance of common stock, net				$ 152,900							$ 0	$ 152,823
Cash dividends declared per common share (usd per share)							$ 0.14	$ 0.14	$ 0.14	$ 0.12	$ 0.42	$ 0.36
Common stock dividends per share declared annualized (usd per share)							$ 0.56	$ 0.56	$ 0.56
US Treasury
Temporary Equity [Line Items]
Warrants outstanding, shares			1,643,295				46,859				46,859
Warrant termination period			10 years
Investment warrants, exercise price (usd per share)											$ 22.66
Warrants exercised, shares											294,993
Common stock shares issued from exercise of warrants											202,325
Common stock
Temporary Equity [Line Items]
Common stock issued, conversion of preferred stock, shares	3,069,828	51,244											729
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	$ 1,000			$ 1,000	$ 1,000	$ 1,000	$ 1,000
Preferred stock, value						$ 126,500	$ 0			$ 126,257	$ 0	$ 126,257	$ 126,257
Preferred stock, dividend rate, percentage						5.00%
Convertible preferred stock, rate of conversion, shares	24.72
Number of shares converted	124,184	2,073											30
London Interbank Offered Rate (LIBOR) | Series D Preferred Stock
Temporary Equity [Line Items]
Preferred stock, dividend rate, percentage, variable spread					4.06%