Investment Securities (Marketable Securities) (Detail) - USD ($)	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 1,676,137,000	$ 1,776,148,000	$ 624,188,000
Gross Unrealized Gains	8,629,000	6,929,000	15,646,000
Gross Unrealized Losses	(35,130,000)	(58,410,000)	(2,171,000)
Available-for-sale securities, at fair value	1,649,636,000	1,724,667,000	637,663,000
Held-to-maturity securities, Amortized Cost	793,376,000	635,705,000	992,211,000
Held-to-maturity securities, Gross Unrealized Gains	2,854,000	654,000	18,828,000
Held-to-maturity securities, Gross Unrealized Losses	(8,741,000)	(28,757,000)	(860,000)
Held-to-maturity securities	787,489,000	607,602,000	1,010,179,000
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	119,804,000	142,741,000	122,296,000
Gross Unrealized Gains	0	1,000	35,000
Gross Unrealized Losses	(723,000)	(759,000)	(1,000)
Available-for-sale securities, at fair value	119,081,000	141,983,000	122,330,000
U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	158,162,000	189,540,000	69,678,000
Gross Unrealized Gains	22,000	47,000	238,000
Gross Unrealized Losses	(674,000)	(435,000)	0
Available-for-sale securities, at fair value	157,510,000	189,152,000	69,916,000
Held-to-maturity securities, Amortized Cost	585,071,000	433,343,000	789,482,000
Held-to-maturity securities, Gross Unrealized Gains	556,000	7,000	11,861,000
Held-to-maturity securities, Gross Unrealized Losses	(7,461,000)	(24,470,000)	(647,000)
Held-to-maturity securities	578,166,000	408,880,000	800,696,000
Municipal Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	121,610,000	129,446,000	108,179,000
Gross Unrealized Gains	2,774,000	2,969,000	3,588,000
Gross Unrealized Losses	(264,000)	(606,000)	(127,000)
Available-for-sale securities, at fair value	124,120,000	131,809,000	111,640,000
Held-to-maturity securities, Amortized Cost	208,305,000	202,362,000	202,729,000
Held-to-maturity securities, Gross Unrealized Gains	2,298,000	647,000	6,967,000
Held-to-maturity securities, Gross Unrealized Losses	(1,280,000)	(4,287,000)	(213,000)
Held-to-maturity securities	209,323,000	198,722,000	209,483,000
Corporate notes, Financial issuers
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	60,340,000	65,260,000	68,097,000
Gross Unrealized Gains	71,000	132,000	1,502,000
Gross Unrealized Losses	(810,000)	(1,000,000)	(1,411,000)
Available-for-sale securities, at fair value	59,601,000	64,392,000	68,188,000
Corporate notes, Other
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	1,000,000	1,000,000	1,500,000
Gross Unrealized Gains	0	0	2,000
Gross Unrealized Losses	(3,000)	(1,000)	0
Available-for-sale securities, at fair value	997,000	999,000	1,502,000
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	1,139,734,000	1,185,448,000	162,593,000
Gross Unrealized Gains	2,301,000	284,000	4,280,000
Gross Unrealized Losses	(31,704,000)	(54,330,000)	(150,000)
Available-for-sale securities, at fair value	1,110,331,000	1,131,402,000	166,723,000
Mortgage-backed, Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	42,845,000	30,105,000	40,419,000
Gross Unrealized Gains	433,000	67,000	457,000
Gross Unrealized Losses	(319,000)	(490,000)	(91,000)
Available-for-sale securities, at fair value	42,959,000	29,682,000	40,785,000
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	32,642,000	32,608,000	51,426,000
Gross Unrealized Gains	3,028,000	3,429,000	5,544,000
Gross Unrealized Losses	(633,000)	(789,000)	(391,000)
Available-for-sale securities, at fair value	35,037,000	35,248,000	56,579,000
Mortgage-backed securities, subprime
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	$ 0	$ 0	$ 0