Fair Value Measurements - Summary of Difference Between Aggregate Fair Value and Remaining Contractual Principal Outstanding for Financial Instruments for which Fair Value Option has been Elected (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Loans held for sale, unpaid principal balance	$ 591,397	$ 375,274
Loans held for sale, fair value	611,277	384,375
Loans held for sale, fair value over/(under) unpaid principal balance	$ 19,880	$ 9,101