Common Share Capitalization (Dividend Distributions) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended			6 Months Ended				6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 First Quarter, Current Period [Member]	Mar. 31, 2012 First Quarter, Current Period [Member]	Jun. 30, 2012 Second Quarter, Current Period [Member]		Jun. 30, 2012 First Quarter, Prior Period [Member]	Mar. 31, 2011 First Quarter, Prior Period [Member]	Jun. 30, 2012 Second Quarter, Prior Period [Member]	Jun. 30, 2011 Second Quarter, Prior Period [Member]
Schedule of Dividends [Line Items]
Dividend Per Share			$ 0.70	$ 0.70			$ 0.40		$ 0.40
Dividend Amount			$ 11,787	$ 11,787	[1]		$ 6,757		$ 6,752
Record Date	Aug. 31, 2012	Jun. 01, 2012		Aug. 31, 2012		Jun. 01, 2011		Sep. 01, 2011
Payment Date	Sep. 17, 2012	Jun. 15, 2012		Sep. 17, 2012		Jun. 15, 2011		Sep. 15, 2011

[1] Estimated