Investment Securities - Gross Unrealized Losses and Fair Value, Aggregated by Investment Category (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 60,388	$ 451,319
Less than 12 months, Unrealized Losses	(81)	(12,439)
12 months or more, Fair Value	80,431	10,271
12 months or more, Unrealized Losses	(2,268)	(601)
Fair Value, Total	140,819	461,590
Gross Unrealized Losses	(2,349)	(13,040)
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	60,388	425,623
Less than 12 months, Unrealized Losses	(81)	(10,061)
12 months or more, Fair Value	80,426	5,274
12 months or more, Unrealized Losses	(2,267)	(598)
Fair Value, Total	140,814	430,897
Gross Unrealized Losses	(2,348)	(10,659)
Corporate notes (2)
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	0	4,982
Less than 12 months, Unrealized Losses	0	(18)
12 months or more, Fair Value	0	4,997
12 months or more, Unrealized Losses	0	(3)
Fair Value, Total	0	9,979
Gross Unrealized Losses	0	(21)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	0	20,714
Less than 12 months, Unrealized Losses	0	(2,360)
12 months or more, Fair Value	5	0
12 months or more, Unrealized Losses	(1)	0
Fair Value, Total	5	20,714
Gross Unrealized Losses	$ (1)	$ (2,360)