Dividends (Dividends Paid) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Dividends [Abstract]
Cash dividend per common share	$ 0.16875	$ 0.16750	$ 0.16625
Total cash dividends paid	$ 11,829	$ 11,516	$ 11,415		$ 34,760	$ 32,866
Record date	Aug. 16, 2013	May 10, 2013	Feb. 22, 2013
Payment date	Sep. 20, 2013	Jun. 14, 2013	Mar. 15, 2013
Cash dividend per common share based on weighted average number of shares	$ 0.17			$ 0.16	$ 0.50	$ 0.49