Stockholders' Equity (Stock Transactions - Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2017	Aug. 14, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Oct. 27, 2017	May 02, 2017	May 01, 2017
Class of Stock [Line Items]
Common stock, authorized shares			300,000,000		300,000,000		150,000,000
Common stock, par value (dollars per share)		$ 0.01	$ 0.01		$ 0.01		$ 0.01
Dividends declared per common share, during the period (in dollars per share)			$ 0.30	$ 0.30	$ 0.90	$ 0.90
Common Stock
Class of Stock [Line Items]
Common stock, authorized shares									300,000,000	150,000,000
At The Market Equity Offering Program
Class of Stock [Line Items]
Issuance of common stock (shares)					0
Subsequent Event
Class of Stock [Line Items]
Dividends declared per common share, during the period (in dollars per share)	$ 0.30
Subsequent Event | At The Market Equity Offering Program
Class of Stock [Line Items]
Number of authorized shares remaining under offering program (shares)								5,868,697
Common Stock
Class of Stock [Line Items]
Issuance of common stock (shares)		8,337,500			8,386,035		14,063,100
Price per share (dollars per share)		$ 30.90
Proceeds from sale of stock		$ 247.1