Short-Term Borrowings - Additional Information (Detail) - FHLB Borrowings [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Amount outstanding at period-end	$ 900,000	$ 515,000
FHLB Borrowings, Maturing in 2017 # 1 [Member]
Short-term Debt [Line Items]
Amount outstanding at period-end	225,000
FHLB Borrowings, Maturing in2017 # 2 [Member]
Short-term Debt [Line Items]
Amount outstanding at period-end	225,000
FHLB Borrowings, Maturing in 2020 # 1 [Member]
Short-term Debt [Line Items]
Amount outstanding at period-end	225,000
FHLB Borrowings, Maturing in 2020 # 2 [Member]
Short-term Debt [Line Items]
Amount outstanding at period-end	$ 225,000