Loans Held for Sale - Composition of Loans Held for Sale (Detail) - USD ($) $ in Thousands		3 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Receivables Held-for-sale [Abstract]
Mortgage warehouse loans, at fair value	$ 1,793,408	$ 1,874,853
Multi-family loans at lower of cost or fair value	144,191	0
Total commercial loans held for sale	1,937,599	1,874,853
Residential mortgage loans, at fair value	1,886	662
Loans held for sale	1,939,485	$ 1,875,515
Loans held for sale, average life from purchase to sale		21 days
Transfer of loans to other real estate owned		$ 129,700
Transfer of loans held for sale to held for investment	$ 150,600	$ 129,691	$ 0