Stockholder's Equity (Details 1) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Summary of common stock issuances
Dividend reinvestment plan issuances, Shares Issued	1,143,397	652,724
Dividend reinvestment plan issuances, Average Price	$ 55.71	$ 61.59
Dividend reinvestment plan issuances, Net Proceeds	63,703,000	40,199,000
Dividend reinvestment plan issuances, Gross Proceeds	63,703,000	40,199,000
Option exercises, Shares	1,155	119,999
Option exercises, Average Price	45.02	43.15
Option exercises, Gross Proceeds	52,000	5,178,000
Option exercises, Net Proceeds	52,000	5,178,000
Issuance of Common Stock, Shares	1,377,788	772,723
Preferred stock conversions	(233,236)	0
Senior note conversions	1
Gross Proceeds From Issuance of Common Stock	63,755,000	45,377,000
Net proceeds from the issuance of common stock	$ 63,755,000	$ 45,377,000