Other Assets and Liabilities - Summary of Components of Other Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Debt securities held-to-maturity	$ 95,877	$ 96,167
Accrued interest receivable	61,148	56,679
Loan portfolio payments held by servicer	39,784	6,133
Derivative assets	5,384	9,916
Collateral deposited under derivative agreements	5,090
Prepaid expenses	512	647
Prepaid taxes	3	6
Other	250	965
Total	$ 208,048	$ 170,513