Comprehensive Income - Impact of Reclassification from AOCI to Retained Earnings (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Increase to retained earnings	$ 64,029
Net Unrealized Losses on Investment Securities [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Increase to retained earnings	8,065
Defined Benefit Plans Liability Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Increase to retained earnings	53,960
Cash Flow Hedges and Other [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Increase to retained earnings	$ 2,004