Schedule of Federal Reserve Bank Stock and Other Securities (Detail) (Federal Reserve Bank Stock and Other Securities [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Other Securities [Line Items]
Amortized Cost	$ 44,917	$ 33,438
Gross Unrealized Gains	22,610	17,044
Gross Unrealized Losses	0
Fair Value	67,527	50,482
Other securities - non-marketable [Member]
Schedule of Other Securities [Line Items]
Amortized Cost	28,638	17,139
Gross Unrealized Gains	2,590	432
Gross Unrealized Losses	0
Fair Value	31,228	17,571
Other securities - marketable [Member]
Schedule of Other Securities [Line Items]
Amortized Cost	0	20
Gross Unrealized Gains	20,020	16,612
Gross Unrealized Losses	0
Fair Value	20,020	16,632
Federal Reserve Bank Stock [Member]
Schedule of Other Securities [Line Items]
Amortized Cost	16,279	16,279
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 16,279	$ 16,279