Shareholders Equity (Narrative) (Details) (USD $)	6 Months Ended			3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Common Shares [Member]	Jun. 30, 2014 At The Market Equity Program [Member]	Jun. 30, 2014 At The Market Equity Program [Member]	Feb. 12, 2014 At The Market Equity Program [Member]	Jun. 30, 2014 At The Market Equity Program [Member] Commissions [Member]	Jun. 30, 2014 At The Market Equity Program [Member] Commissions [Member]	Jun. 30, 2014 At The Market Equity Program [Member] Other Offering Costs [Member]	Jun. 30, 2014 At The Market Equity Program [Member] Other Offering Costs [Member]
Aggregate offering price of common share						$ 300,000,000
Shares issued under equity program			896,545	440,778	896,490
Weighted average price per common share				$ 119.66	$ 115.44
Net cash proceeds of common stock	103,931,000	83,220,000		52,200,000	102,300,000
Payments of stock issuance costs							500,000	1,000,000	100,000	100,000
Remaining Capacity To Issue				$ 196,500,000	$ 196,500,000