Fair Value - Quantitative Information About Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs Assets Quantitative Information [Line Items]
Loans held for sale, at fair value	$ 83,541	$ 62,593
Construction [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Loans held for sale, at fair value	83,541	62,593
Fair Value, Measurements, Recurring [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Loans held for sale, at fair value	83,541	62,593
Fair Value, Measurements, Recurring [Member] | Comparable Sales [Member] | Construction [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Loans held for sale, at fair value	$ 65,016	$ 53,761
Fair Value, Measurements, Recurring [Member] | Comparable Sales [Member] | Minimum [Member] | Construction [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Fair Value Inputs, Time discount using the 60 day forward contract	0.00%	0.00%
Fair Value, Measurements, Recurring [Member] | Comparable Sales [Member] | Maximum [Member] | Construction [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Fair Value Inputs, Time discount using the 60 day forward contract	1.96%	1.80%