Available-For-Sale Securities (Schedule of Available-for-Sale Securities Reconciliation) (Detail) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 2,205,522	$ 1,807,913	$ 1,864,123
Gross Unrealized Gains		18,487	22,145	21,909
Gross Unrealized Losses		(61,948)	(37,980)	(61,792)
Available-for-sale Securities		2,162,061	1,792,078	1,824,240
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		288,196	388,713	399,031
Gross Unrealized Gains		138	84	354
Gross Unrealized Losses		(7,173)	(6,992)	(10,970)
Available-for-sale Securities		281,161	381,805	388,415
U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		651,737	686,106	798,889
Gross Unrealized Gains		2,074	4,113	4,458
Gross Unrealized Losses		(25,151)	(21,903)	(37,347)
Available-for-sale Securities		628,660	668,316	766,000
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		269,562	234,951	173,664
Gross Unrealized Gains		4,222	5,318	4,385
Gross Unrealized Losses		(3,994)	(1,740)	(1,942)
Available-for-sale Securities		269,790	238,529	176,107
Corporate notes, Financial issuers
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		124,924	129,309	129,211
Gross Unrealized Gains		1,773	2,006	2,402
Gross Unrealized Losses		(1,289)	(1,557)	(1,387)
Available-for-sale Securities		125,408	129,758	130,226
Corporate notes, Other
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,726	3,766	4,980
Gross Unrealized Gains		9	55	97
Gross Unrealized Losses		(2)	0	0
Available-for-sale Securities		2,733	3,821	5,077
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1]	777,087	271,129	255,082
Gross Unrealized Gains	[1]	4,053	5,448	5,190
Gross Unrealized Losses	[1]	(23,499)	(4,928)	(9,097)
Available-for-sale Securities	[1]	757,641	271,649	251,175
Mortgage-backed, Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1]	42,550	47,347	52,672
Gross Unrealized Gains	[1]	342	249	389
Gross Unrealized Losses	[1]	(432)	(535)	(673)
Available-for-sale Securities	[1]	42,460	47,061	52,388
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		48,740	46,592	50,594
Gross Unrealized Gains		5,876	4,872	4,634
Gross Unrealized Losses		(408)	(325)	(376)
Available-for-sale Securities		54,208	$ 51,139	$ 54,852
Mortgage-backed securities, subprime
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		$ 0

[1] Consisting entirely of residential mortgage-backed securities, none of which are subprime.