Fair Value Measurements (Summary of Carrying Value and Fair Value of the Company's Financial Instruments Disclosed but not Carried at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable	$ 371,734	$ 371,335
Borrowings [Member] | Unsecured Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable	371,734	371,335
Notes payable, fair value	362,674
Borrowings [Member] | Unsecured Debt [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable, fair value	0	0
Borrowings [Member] | Unsecured Debt [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable, fair value	362,674	385,583
Borrowings [Member] | Unsecured Debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable, fair value	$ 0	$ 0