Equity Transactions - Additional Information (Detail) $ / shares in Units, $ in Thousands				3 Months Ended		9 Months Ended
	Oct. 15, 2017 $ / shares	Aug. 16, 2017 $ / shares	Jun. 01, 2017 shares	Sep. 30, 2017 $ / shares shares	Sep. 30, 2016 $ / shares	Sep. 30, 2017 USD ($) day $ / shares shares	Sep. 30, 2016 USD ($) $ / shares	Feb. 01, 2020 shares
Equity, Class of Treasury Stock [Line Items]
Repurchases of common shares (in shares)						66,244
Common stock cash dividends declared per share (in $ per share) | $ / shares		$ 0.45		$ 0.45	$ 0.45	$ 1.35	$ 1.35
Preferred stock cash dividends declared per share (in $ per share) | $ / shares				$ 1.81	$ 0	5.4375	$ 0
Weighted average price of shares repurchased (in dollars per share) | $ / shares						$ 113.21
Total cost of shares repurchased during the period | $						$ 7,502	$ 72,216
Shares available for repurchase (in shares)				133,756		133,756
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) | $ / shares				$ 100		$ 100
Convertible preferred stock, threshold consecutive trading days | day						20
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 | $						$ 111,000
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 | $						$ 109,500
Public offering 2 | Common stock
Equity, Class of Treasury Stock [Line Items]
Common stock issued (in shares)						1,046,500
Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Preferred stock cash dividends declared per share (in $ per share) | $ / shares	$ 1.8125