Equity and Capital - Repayment of Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Parent Company [Member]
Extinguishment of Debt [Line Items]
Stock Issued During Period, Shares, New Issues		13,000,000
Repayment of fixed rate unsecured notes	$ 300,000	$ 450,000	$ 150,000
Proceeds from Issuance of Common Stock	$ 548,920	$ 198,494	$ 102,453
Forward Equity Offering [Member]
Extinguishment of Debt [Line Items]
Stock Issued During Period, Shares, New Issues	1,850,000
Proceeds from Issuance of Common Stock	$ 137,500
Maximum [Member]
Extinguishment of Debt [Line Items]
Forward Equity Offering, Common Shares available for issue	1,250,000