Fair Value Measurements - Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 138,482	$ 94,023
Specific valuation allowance allocations	(14,932)	$ (9,186)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	0		$ 0
Specific valuation allowance allocations	0		0
Loans receivable, fair value disclosure	0		0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	64,287		11,023
Specific valuation allowance allocations	(13,477)		(3,750)
Loans receivable, fair value disclosure	$ 50,810		$ 7,273