Fair Value Measurements (Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 70,221	$ 145,610	$ 94,023
Specific valuation allowance allocations	(16,235)	(20,820)	(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	12,517	0	0
Specific valuation allowance allocations	(2,599)	0	0
Fair value	9,918	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	22,688	75,435	33,626
Reversal of specific valuation allowance allocations	9,260
Specific valuation allowance allocations		(19,533)	(3,961)
Fair value	$ 31,948	$ 55,902	$ 29,665