Shareholders Equity (Narrative) (Details) (USD $)	9 Months Ended		3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 At The Market Equity Program	Sep. 30, 2014 At The Market Equity Program	Feb. 12, 2014 At The Market Equity Program	Sep. 30, 2014 At The Market Equity Program Commissions	Sep. 30, 2014 At The Market Equity Program Commissions	Sep. 30, 2014 At The Market Equity Program Additional offering expenses	Sep. 30, 2014 At The Market Equity Program Additional offering expenses
Aggregate offering price of common share					$ 300,000,000
Shares issued under equity program			402,893	1,299,383
Weighted average price per common share			$ 124.71	$ 118.31
Net cash proceeds of common stock	154,250,000	118,087,000	49,700,000	152,000,000
Payments of stock issuance costs						500,000	1,500,000	100,000	200,000
Remaining capacity of common shares to issue			$ 146,300,000	$ 146,300,000