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
	Aug. 25, 2016	Aug. 11, 2016	May 26, 2016	May 12, 2016	Feb. 25, 2016	Feb. 11, 2016	Dec. 19, 2008	Jul. 31, 2016	Jun. 30, 2016	Apr. 30, 2016	Jan. 31, 2016	Jul. 31, 2015	Jun. 30, 2015	Jan. 31, 2015	Mar. 31, 2012	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Temporary Equity [Line Items]
Stock issued in public offering, shares									3,000,000
Proceeds from the issuance of common stock, net									$ 152,800									$ 152,823	$ 0
Cash dividends declared per common share (usd per share)								$ 0.12		$ 0.12	$ 0.12					$ 0.12	$ 0.11	$ 0.36	$ 0.33
Common stock dividends per share declared annualized (usd per share)								$ 0.48		$ 0.48	$ 0.48
Dividends payable, date to be paid	Aug. 25, 2016		May 26, 2016		Feb. 25, 2016
Dividends payable, date of record		Aug. 11, 2016		May 12, 2016		Feb. 11, 2016
Community Financial Shares, Inc.
Temporary Equity [Line Items]
Common stock, acquisition, shares issued												388,573
Delavan Bancshares
Temporary Equity [Line Items]
Common stock, acquisition, shares issued														422,122
US Treasury
Temporary Equity [Line Items]
Warrants outstanding, shares							1,643,295									365,829		365,829
Investment warrants, exercise price (usd per share)							$ 22.82
Warrant termination period							10 years
Warrants exercised, shares																		1,603
Common Stock Shares Issued From Exercise Of Warrant Shares																		944
Series D Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares issued													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 payment terms													quarterly
Preferred stock, dividend rate, percentage													6.50%
Series C Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares issued															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	$ 126,257	$ 126,312	$ 126,257	$ 126,312	$ 126,287
Preferred stock, Dividend payment terms															quarterly
Preferred stock, dividend rate, percentage															5.00%
Convertible preferred stock, rate of conversion, shares															24.5569
Preferred stock, shares converted																		30		180
Common stock, conversion of preferred stock, shares																		729		4,374
London Interbank Offered Rate (LIBOR) | Series D Preferred Stock
Temporary Equity [Line Items]
Preferred stock, dividend rate, percentage, variable spread													4.06%