Securities (Detail) - Remaining Contractual Maturity of Securities - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
One year or less	$ 95,201
After one year to five years	272,169
After five years to ten years	57,528
After ten years	48,287
Securities that do not have a single contractual maturity date	850,961
Amortized Cost	1,324,146	$ 1,192,322
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	93,096
After one year to five years	266,151
After five years to ten years	56,256
After ten years	47,219
Securities that do not have a single contractual maturity date	843,914
Total	1,306,636	1,187,009
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
One year or less	2,092
After one year to five years	8,809
After five years to ten years	4,184
After ten years	8,067
Securities that do not have a single contractual maturity date	0
Total	23,152	26,555
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	1,812
After one year to five years	7,630
After five years to ten years	3,624
After ten years	6,988
Securities that do not have a single contractual maturity date	0
Total	$ 20,054	$ 27,670