Common Stock and Related Matters (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Jun. 30, 2013	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Common Stock and Related Matters [Abstract]
Date paid or to be paid		May 16, 2013		Feb. 15, 2013
Total dividend declared		$ 21.0		$ 19.4
Amount of dividend paid	20.6	19.0		19.0		13.8
Accrued dividends		$ 0.4	[1]	$ 0.4	[1]
Dividend declared per share of common stock (in dollars per share)		$ 0.49500		$ 0.45750

[1] Represents accrued dividends on the restricted shares that are payable upon vesting.