Fair Value Measurements - Carrying Value and Estimated Fair Value of Notes Payable (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable(4)	$ 48,759
Carrying value	906,608	$ 857,842
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable(4)	942,427	882,813
Fair Value | Quoted Price in Active Markets for Identical Assets and Liabilities (Level 1)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable(4)	0	0
Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable(4)	0	0
Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable(4)	942,427	882,813
Reported Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Carrying value	$ 906,608	$ 857,842