Fair Value of Financial Instruments - Schedule of Debt Instruments Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Unsecured senior notes | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unsecured Senior Notes	$ 0	$ 0
Unsecured senior notes | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unsecured Senior Notes	0	0
Unsecured senior notes | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unsecured Senior Notes	53,800	52,700
Unsecured senior notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unsecured Senior Notes	55,000	55,000
Unsecured senior notes | Unsecured senior notes | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unsecured Senior Notes	54,782	54,712
Wells Fargo revolving credit facility | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Wells Fargo Credit Agreement	0	0
Wells Fargo revolving credit facility | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Wells Fargo Credit Agreement	0	0
Wells Fargo revolving credit facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Short-Term Debt	56,825	54,613
Wells Fargo revolving credit facility | Wells Fargo revolving credit facility | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Short-Term Debt	56,825	54,613
Wells Fargo revolving credit facility | Wells Fargo revolving credit facility | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Short-Term Debt	$ 56,825	$ 54,613