Repurchase Agreements - Summary of Repurchase Agreements Accounted as Secured Borrowings (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	$ 154,399
Securities lending transactions, Total	170,777
Total borrowings	(16,378)
Gross amount of recognized liabilities for repurchase agreements and securities lending	154,399
U.S. Treasury and Federal Agencies [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	5,468
Federal Agency Collateralized Mortgage Obligations [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	99,174
Federal Agency Mortgage-backed Pools [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	66,135
Remaining Contractual Maturity of the Agreements, Overnight and Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	59,399
Securities lending transactions, Total	65,511
Total borrowings	(6,112)
Remaining Contractual Maturity of the Agreements, Overnight and Continuous [Member] | U.S. Treasury and Federal Agencies [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	5,468
Remaining Contractual Maturity of the Agreements, Overnight and Continuous [Member] | Federal Agency Collateralized Mortgage Obligations [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	45,975
Remaining Contractual Maturity of the Agreements, Overnight and Continuous [Member] | Federal Agency Mortgage-backed Pools [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	14,068
Remaining Contractual Maturity of the Agreements, One to Three Years [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	35,000
Securities lending transactions, Total	844
Total borrowings	34,156
Remaining Contractual Maturity of the Agreements, One to Three Years [Member] | Federal Agency Collateralized Mortgage Obligations [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	609
Remaining Contractual Maturity of the Agreements, One to Three Years [Member] | Federal Agency Mortgage-backed Pools [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	235
Remaining Contractual Maturity of the Agreements, Three to Five Years [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	60,000
Securities lending transactions, Total	523
Total borrowings	59,477
Remaining Contractual Maturity of the Agreements, Three to Five Years [Member] | Federal Agency Collateralized Mortgage Obligations [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	213
Remaining Contractual Maturity of the Agreements, Three to Five Years [Member] | Federal Agency Mortgage-backed Pools [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	310
Remaining Contractual Maturity of the Agreements, Five to Ten Years [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	34,944
Total borrowings	(34,944)
Remaining Contractual Maturity of the Agreements, Five to Ten Years [Member] | Federal Agency Collateralized Mortgage Obligations [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	19,063
Remaining Contractual Maturity of the Agreements, Five to Ten Years [Member] | Federal Agency Mortgage-backed Pools [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	15,881
Remaining Contractual Maturity of the Agreements, Beyond Ten Years [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	68,955
Total borrowings	(68,955)
Remaining Contractual Maturity of the Agreements, Beyond Ten Years [Member] | Federal Agency Collateralized Mortgage Obligations [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	33,314
Remaining Contractual Maturity of the Agreements, Beyond Ten Years [Member] | Federal Agency Mortgage-backed Pools [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions, Total	$ 35,641