Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Mortgage Backed Securities [Member]		Jun. 30, 2013 Mortgage Backed Securities [Member]		Jun. 30, 2014 US Government Agencies Residential Mortgage-backed Securities [Member]	Dec. 31, 2013 US Government Agencies Residential Mortgage-backed Securities [Member]	Jun. 30, 2014 Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment Securities [Line Items]
Due within one year, Amortized Cost	$ 2,600
Due after one but within five years, Amortized Cost	266,575
Due after five but within ten years, Amortized Cost	8,402
Due after ten years, Amortized Cost	55,875
Debt securities gross, Amortized Cost	333,452
Corporate/Mortgage-Backed Securities, Amortized cost	1,357,315	1,350,466	1,022,443	[1]	1,026,512	[1]	20,686	22,639	1,001,800
Debt Securities, Amortized Cost	1,355,895
Due within one year, Estimated Fair Value	2,601
Due after one but within five years, Estimated Fair Value	265,786
Due after five but within ten years, Estimated Fair Value	8,506
Due after ten years, Estimated Fair Value	42,786
Debt securities gross, Estimated Fair Value	319,679
Total Debt Securities, Estimated Fair Value	$ 1,346,191

[1] Mortgage Backed Securities include an amortized cost of $20.7 million and a fair value of $23.3 million for Obligations of U.S.