Fair Value Measurements - Amount of Net Gains (Losses) from Fair Value Changes (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Net Gains (Losses) Resulting From Changes in Fair Value - Mortgage loans held for sale, at fair value	$ 652	$ (749)
Net Gains (Losses) Resulting From Changes in Fair Value - Mortgage loans held for investment, at fair value	$ 191	$ (1,142)

Net Gains Losses From Change In Fair Value Of Mortgages Loans Held For Investment

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