Fair Value Measurements - Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 94,770	$ 70,221
Specific valuation allowance allocations	(29,160)	$ (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	2,416		$ 12,876
Specific valuation allowance allocations	1,116		(2,599)
Loans receivable, fair value disclosure	3,532		10,277
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	60,010		28,638
Specific valuation allowance allocations	(12,437)		4,256
Loans receivable, fair value disclosure	$ 47,573		$ 32,894