Equity and Capital Equity and Capital - Common Stock (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jan. 15, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Document Fiscal Year Focus	2015
Amount reclassified from accumulated other comprehensive loss	$ (2,249,000)	$ (2,519,000)
Shares issued	18,125	0
Equity Issuances, Amount Available for Issuance	95,000,000
Document Period End Date	Mar. 31, 2015
Equity Offering, Common Shares available for issue			2,875,000
Weighted Average Price Per Share	$ 64.72
Net proceeds from common stock issuance	1,173,000
Payments for Commissions	15,000
Payments of Stock Issuance Costs	0
Equity Offering, Net Proceeds	193,800,000
Maximum [Member]
Class of Stock [Line Items]
Equity Issuances, Amount Available for Issuance	200,000,000
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Class of Stock [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	2,249,000	2,519,000
Accumulated Other Comprehensive Income (Loss) [Member]
Class of Stock [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	2,249,000	2,519,000
Accumulated other comprehensive loss	$ (70,131,000)	$ (29,164,000)		$ (58,498,000)	$ (17,883,000)