Fair Value Measurements Summary of Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Recorded value	$ 1,823,040	$ 1,065,180
Deferred financing costs	16,042	9,024
Fair Value Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair value	$ 1,765,151	$ 1,056,990