Securities Available for Sale - Securities Available for Sale by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 957,938	$ 1,061,461
Securities available for sale, at fair value	964,534	$ 1,074,395
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, amortized cost	27,044
Due after one year through five years, amortized cost	67,106
Due after five years through ten years, amortized cost	3,681
Due after ten years, amortized cost	2,280
Amortized cost	100,111
Due in one year or less, fair value	27,058
Due after one year through five years, fair value	67,037
Due after five years through ten years, fair value	3,701
Due after ten years, fair value	2,358
Securities available for sale, at fair value	$ 100,154