Fair Value Measurements - Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 89,115	$ 70,221
Specific valuation allowance allocations	(19,973)	$ (16,235)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	11,487		$ 365
Specific valuation allowance allocations	(256)		(64)
Loans receivable, fair value disclosure	11,231		301
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	37,525		56,788
Specific valuation allowance allocations	(3,441)		(1,520)
Loans receivable, fair value disclosure	$ 34,084		$ 55,268