Common Stock and Related Matters (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Dividend declared, Q1 2014 [Member]		Dec. 31, 2013 Dividend Declared, Q4 2013 [Member]
Dividends Payable [Line Items]
Date paid or to be paid			May 16, 2014		Feb. 18, 2014
Total dividend declared			$ 27.4		$ 25.6
Amount of dividend to be paid			27.2
Amount of dividend paid	25.5	19.0			25.5
Accrued dividends			$ 0.2	[1]	$ 0.1	[1]
Dividend declared per share of common stock (in dollars per share)			$ 0.64750		$ 0.60750

[1] Represents accrued dividends on restricted stock and restricted stock units that are payable upon vesting.