Fair Value Measurement - Quantitative Information About Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Construction loans held for sale, at fair value	$ 77,676	$ 91,472
Construction [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Construction loans held for sale, at fair value	77,676	91,472
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Construction loans held for sale, at fair value	77,676	91,472
Fair Value, Measurements, Recurring [Member] | Comparable Sales [Member] | Construction [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Construction loans held for sale, at fair value	$ 65,796	$ 80,251
Fair Value, Measurements, Recurring [Member] | Comparable Sales [Member] | Construction [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value Inputs, Time discount	0.00%	0.00%
Fair Value, Measurements, Recurring [Member] | Comparable Sales [Member] | Construction [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value Inputs, Time discount	1.13%	1.05%