Equity Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Feb. 15, 2017	Mar. 31, 2017	Mar. 31, 2016	Feb. 01, 2020	Feb. 01, 2017
Equity, Class of Treasury Stock [Line Items]
Common stock available to repurchase (in shares)		200,000
Common stock authorized to be repurchased (in shares)		3,430,045
Proceeds from stock issuance		$ 220.1
Common stock cash dividends declared per share (in $ per share)	$ 0.45	$ 0.45	$ 0.45
Preferred stock cash dividends declared per share (in $ per share)	$ 1.8125	$ 1.8125	$ 0
Common stock
Equity, Class of Treasury Stock [Line Items]
Common stock issued (in shares)		1,046,500
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%
Convertible preferred stock liquidation preference (in dollars per share)		$ 100.00			$ 100.00
Convertible preferred stock, threshold consecutive trading days		20 days
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