Summary of Significant Accounting Policies Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Percent distribution of REIT taxable income	100.00%
Income provision	$ 0
Number of years subequent to a failed REIT Qualifing Test the Company would not be Qualified as a REIT	4 years
Uncertain tax positions	$ 0
Penalties and interest	0	$ 0	$ 0
Penalties and interest accrued	0	0
Federal income tax basis	6,800,000,000	$ 6,500,000,000
Taxable REIT Subsidiary [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	40,600,000
Valuation allowance	$ 40,600,000
Expiration dates	Jan. 01, 2018
Tax Year 2018 [Member] | Tax Cuts and Jobs Act [Member] | Taxable REIT Subsidiary [Member]
Income Tax Contingency [Line Items]
Effective income tax rate	21.00%
Cash [Member] | Tax Year 2018 [Member] | Tax Cuts and Jobs Act [Member] | Taxable REIT Subsidiary [Member]
Income Tax Contingency [Line Items]
Effective income tax rate for repatriation of foreign earnings	15.50%
Noncash [Member] | Tax Year 2018 [Member] | Tax Cuts and Jobs Act [Member] | Taxable REIT Subsidiary [Member]
Income Tax Contingency [Line Items]
Effective income tax rate for repatriation of foreign earnings	8.00%