Equity Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended
	Jun. 01, 2017	May 19, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Feb. 01, 2020
Equity, Class of Treasury Stock [Line Items]
Common stock cash dividends declared per share (in $ per share)		$ 0.45	$ 0.45	$ 0.45	$ 0.90	$ 0.90
Preferred stock cash dividends declared per share (in $ per share)		$ 1.8125	$ 1.81	$ 0	$ 3.625	$ 0
Shares available for repurchase (in shares)			200,000		200,000
Shares authorized for repurchase (in shares)			3,430,045		3,430,045
Convertible preferred stock
Equity, Class of Treasury Stock [Line Items]
Convertible preferred stock liquidation preference (in dollars per share)			$ 100		$ 100
Convertible preferred stock, threshold consecutive trading days					20 days
Common stock
Equity, Class of Treasury Stock [Line Items]
Common stock issued (in shares)					1,260,169
Minimum | Forecast | Convertible preferred stock
Equity, Class of Treasury Stock [Line Items]
Convertible preferred stock, shares issued upon conversion (in shares)							0.7576
Maximum | Forecast | Convertible preferred stock
Equity, Class of Treasury Stock [Line Items]
Convertible preferred stock, shares issued upon conversion (in shares)							0.9091
RidgeWorth
Equity, Class of Treasury Stock [Line Items]
Purchase price, shares issued (in shares)	213,669
Public offering 1
Equity, Class of Treasury Stock [Line Items]
Proceeds from stock issuance					$ 111.0
Public offering 1 | Convertible preferred stock
Equity, Class of Treasury Stock [Line Items]
Common stock issued (in shares)					1,150,000
Convertible preferred stock dividend rate					7.25%
Public offering 2
Equity, Class of Treasury Stock [Line Items]
Proceeds from stock issuance					$ 109.5
Public offering 2 | Common stock
Equity, Class of Treasury Stock [Line Items]
Common stock issued (in shares)					1,046,500