Investment Securities (Marketable Securities) (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 1,637,399,000	$ 1,731,292,000	$ 2,226,376,000
Gross Unrealized Gains	15,136,000	14,766,000	20,153,000
Gross Unrealized Losses	(2,439,000)	(29,670,000)	(32,248,000)
Available-for-sale securities, Fair Value	1,650,096,000	1,716,388,000	2,214,281,000
Held-to-maturity securities, Amortized Cost	932,767,000	884,826,000	0
Held-to-maturity securities, Gross Unrealized Gains	13,092,000	871,000	0
Held-to-maturity securities, Gross Unrealized Losses	(3,193,000)	(7,586,000)	0
Held-to-maturity securities	942,666,000	878,111,000	0
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	30,017,000	312,282,000	288,185,000
Gross Unrealized Gains	19,000	0	101,000
Gross Unrealized Losses	0	(5,553,000)	(2,364,000)
Available-for-sale securities, Fair Value	30,036,000	306,729,000	285,922,000
U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	93,561,000	70,313,000	657,297,000
Gross Unrealized Gains	163,000	198,000	2,726,000
Gross Unrealized Losses	(41,000)	(275,000)	(15,000,000)
Available-for-sale securities, Fair Value	93,683,000	70,236,000	645,023,000
Held-to-maturity securities, Amortized Cost	729,417,000	687,302,000	0
Held-to-maturity securities, Gross Unrealized Gains	7,577,000	4,000	0
Held-to-maturity securities, Gross Unrealized Losses	(2,879,000)	(7,144,000)	0
Held-to-maturity securities	734,115,000	680,162,000	0
Municipal
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	106,033,000	105,702,000	294,073,000
Gross Unrealized Gains	3,395,000	3,249,000	5,354,000
Gross Unrealized Losses	(147,000)	(356,000)	(2,085,000)
Available-for-sale securities, Fair Value	109,281,000	108,595,000	297,342,000
Held-to-maturity securities, Amortized Cost	203,350,000	197,524,000	0
Held-to-maturity securities, Gross Unrealized Gains	5,515,000	867,000	0
Held-to-maturity securities, Gross Unrealized Losses	(314,000)	(442,000)	0
Held-to-maturity securities	208,551,000	197,949,000	0
Corporate notes, Financial issuers
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	65,215,000	80,014,000	114,976,000
Gross Unrealized Gains	299,000	1,510,000	1,656,000
Gross Unrealized Losses	(1,311,000)	(1,481,000)	(1,216,000)
Available-for-sale securities, Fair Value	64,203,000	80,043,000	115,416,000
Corporate notes, Other
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	1,000,000	1,500,000	1,525,000
Gross Unrealized Gains	0	4,000	6,000
Gross Unrealized Losses	0	(2,000)	(2,000)
Available-for-sale securities, Fair Value	1,000,000	1,502,000	1,529,000
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	1,257,070,000	1,069,680,000	778,240,000
Gross Unrealized Gains	7,958,000	3,834,000	4,974,000
Gross Unrealized Losses	(54,000)	(21,004,000)	(10,913,000)
Available-for-sale securities, Fair Value	1,264,974,000	1,052,510,000	772,301,000
Mortgage-backed, Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	35,935,000	40,421,000	42,724,000
Gross Unrealized Gains	304,000	172,000	343,000
Gross Unrealized Losses	(102,000)	(506,000)	(323,000)
Available-for-sale securities, Fair Value	36,137,000	40,087,000	42,744,000
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	48,568,000	51,380,000	49,356,000
Gross Unrealized Gains	2,998,000	5,799,000	4,993,000
Gross Unrealized Losses	(784,000)	(493,000)	(345,000)
Available-for-sale securities, Fair Value	50,782,000	56,686,000	54,004,000
Mortgage-backed securities, subprime
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Fair Value	$ 0	$ 0	$ 0