Borrowed Funds - Remaining Contractual Maturities Of Repurchase Agreements (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	$ 2,249,861	$ 1,864,635
2 to 29 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	1,759,559	1,753,870
30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	489,302	110,765
Over 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	1,000
U.S. Treasury [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	2,440
U.S. Treasury [Member] | 2 to 29 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	2,440
U.S. Agencies [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	2,247,421	1,864,635
U.S. Agencies [Member] | 2 to 29 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	1,757,119	1,753,870
U.S. Agencies [Member] | 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	489,302	$ 110,765
U.S. Agencies [Member] | Over 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	$ 1,000