Stockholders' Equity - Preferred Stock and Dividend Payments (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions			12 Months Ended
	Jun. 30, 2015	Mar. 30, 2015	Dec. 31, 2015
Preferred Stock and Dividend Payments
Preferred stock redemption			$ 550.0
Excess of redemption value over carrying value of preferred shares redeemed			8.2
Dividends to preferred stockholders			$ 16.5
Preferred stock
Preferred Stock and Dividend Payments
Excess of redemption value over carrying value of preferred shares redeemed	$ 8.2
Dividends to preferred stockholders	$ 8.3	$ 8.2
Series A | Preferred stock
Preferred Stock and Dividend Payments
Preferred stock redemption (in shares)	3.0		3.0
Preferred stock redemption	$ 300.0
Preferred stock dividend (in dollars per share)	$ 1.39	$ 1.39
Series B | Preferred stock
Preferred Stock and Dividend Payments
Preferred stock redemption (in shares)	10.0		10.0
Preferred stock redemption	$ 250.0
Preferred stock dividend (in dollars per share)	$ 0.41	$ 0.41