Dividends (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	0 Months Ended													12 Months Ended
	Oct. 29, 2013	Aug. 02, 2013	May 01, 2013	Feb. 18, 2013	Nov. 05, 2012	Aug. 01, 2012	May 02, 2012	Feb. 17, 2012	Nov. 07, 2011	Sep. 14, 2011	Jun. 27, 2011	Mar. 08, 2011	Dec. 06, 2010	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Dividends [Abstract]
Dividend per Common Share	$ 0.200	$ 0.165	$ 0.165	$ 0.165	$ 0.165	$ 0.150	$ 0.150	$ 0.150	$ 0.150	$ 0.125	$ 0.125	$ 0.100	$ 0.100	$ 0.695	$ 0.615	$ 0.50
Aggregate Dividend Amount	$ 16,163	$ 13,330	$ 11,297	$ 11,268	$ 11,493	$ 10,464	$ 10,847	$ 10,865	$ 10,839	$ 9,035	$ 9,364	$ 7,857	$ 7,964	$ 52,058	$ 43,669	$ 37,095