Equity Transactions - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
	Aug. 14, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity, Class of Treasury Stock [Line Items]
Common stock cash dividends declared per share (in $ per share)	$ 0.55	$ 0.55	$ 0.45	$ 1.45	$ 1.35
Preferred stock cash dividends declared per share (in $ per share)	$ 1.8125	$ 1.81	$ 1.81	$ 5.44	$ 5.44
Shares available for repurchase (in shares)		784,950		784,950
Shares authorized for repurchase (in shares)		4,180,045		4,180,045
Repurchases of common shares (in shares)				98,806
Weighted average price (in dollars per share)				$ 126.49
Total cost of shares repurchased				$ 12.5
Public offering 1 | Convertible preferred stock
Equity, Class of Treasury Stock [Line Items]
Convertible preferred stock dividend rate				7.25%