Fair Value of Financial Instruments Carrying Amount and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Secured notes payable | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 161,879	$ 182,572
Secured notes payable | Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	166,885	183,253
Unsecured debt | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	248,864	248,765
Unsecured debt | Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	250,000	250,000
Unsecured senior guaranteed notes | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	946,916	797,098
Unsecured senior guaranteed notes | Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	975,291	790,267
Unsecured line of credit | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	62,337
Unsecured line of credit | Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 0	$ 64,000