Investment Securities (Marketable Securities) (Detail) - USD ($)	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 624,188,000	$ 1,731,292,000	$ 2,205,522,000
Gross Unrealized Gains	15,646,000	14,766,000	18,487,000
Gross Unrealized Losses	(2,171,000)	(29,670,000)	(61,948,000)
Available-for-sale securities, Fair Value	637,663,000	1,716,388,000	2,162,061,000
Held-to-maturity securities, Amortized Cost	992,211,000	884,826,000	0
Held-to-maturity securities, Gross Unrealized Gains	18,828,000	871,000	0
Held-to-maturity securities, Gross Unrealized Losses	(860,000)	(7,586,000)	0
Held-to-maturity securities, Fair Value	1,010,179,000	878,111,000	0
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	122,296,000	312,282,000	288,196,000
Gross Unrealized Gains	35,000	0	138,000
Gross Unrealized Losses	(1,000)	(5,553,000)	(7,173,000)
Available-for-sale securities, Fair Value	122,330,000	306,729,000	281,161,000
U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	69,678,000	70,313,000	651,737,000
Gross Unrealized Gains	238,000	198,000	2,074,000
Gross Unrealized Losses	0	(275,000)	(25,151,000)
Available-for-sale securities, Fair Value	69,916,000	70,236,000	628,660,000
Held-to-maturity securities, Amortized Cost	789,482,000	687,302,000	0
Held-to-maturity securities, Gross Unrealized Gains	11,861,000	4,000	0
Held-to-maturity securities, Gross Unrealized Losses	(647,000)	(7,144,000)	0
Held-to-maturity securities, Fair Value	800,696,000	680,162,000	0
Municipal
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	108,179,000	105,702,000	269,562,000
Gross Unrealized Gains	3,588,000	3,249,000	4,222,000
Gross Unrealized Losses	(127,000)	(356,000)	(3,994,000)
Available-for-sale securities, Fair Value	111,640,000	108,595,000	269,790,000
Held-to-maturity securities, Amortized Cost	202,729,000	197,524,000	0
Held-to-maturity securities, Gross Unrealized Gains	6,967,000	867,000	0
Held-to-maturity securities, Gross Unrealized Losses	(213,000)	(442,000)	0
Held-to-maturity securities, Fair Value	209,483,000	197,949,000	0
Corporate notes, Financial issuers
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	68,097,000	80,014,000	124,924,000
Gross Unrealized Gains	1,502,000	1,510,000	1,773,000
Gross Unrealized Losses	(1,411,000)	(1,481,000)	(1,289,000)
Available-for-sale securities, Fair Value	68,188,000	80,043,000	125,408,000
Corporate notes, Other
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	1,500,000	1,500,000	2,726,000
Gross Unrealized Gains	2,000	4,000	9,000
Gross Unrealized Losses	0	(2,000)	(2,000)
Available-for-sale securities, Fair Value	1,502,000	1,502,000	2,733,000
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	162,593,000	1,069,680,000	777,087,000
Gross Unrealized Gains	4,280,000	3,834,000	4,053,000
Gross Unrealized Losses	(150,000)	(21,004,000)	(23,499,000)
Available-for-sale securities, Fair Value	166,723,000	1,052,510,000	757,641,000
Mortgage-backed, Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	40,419,000	40,421,000	42,550,000
Gross Unrealized Gains	457,000	172,000	342,000
Gross Unrealized Losses	(91,000)	(506,000)	(432,000)
Available-for-sale securities, Fair Value	40,785,000	40,087,000	42,460,000
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	51,426,000	51,380,000	48,740,000
Gross Unrealized Gains	5,544,000	5,799,000	5,876,000
Gross Unrealized Losses	(391,000)	(493,000)	(408,000)
Available-for-sale securities, Fair Value	56,579,000	56,686,000	54,208,000
Mortgage-backed securities, subprime
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Fair Value	$ 0	$ 0	$ 0