Debt and Equity Securities (Gross Unrealized Losses) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	$ 594,101	$ 1,580,179
Unrealized losses, Less than 12 months	(3,144)	(41,734)
Estimated fair value, 12 months or longer	704,494	177,875
Unrealized losses, 12 months or longer	(16,661)	(8,174)
Estimated fair value, Total	1,298,595	1,758,054
Unrealized losses, Total	(19,805)	(49,908)
Equity Securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	8,749	85,112
Unrealized losses, Less than 12 months	(414)	(2,718)
Estimated fair value, 12 months or longer	4,805	1,046
Unrealized losses, 12 months or longer	(247)	(42)
Estimated fair value, Total	13,554	86,158
Unrealized losses, Total	(661)	(2,760)
Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	585,352	1,495,067
Unrealized losses, Less than 12 months	(2,730)	(39,016)
Estimated fair value, 12 months or longer	699,689	176,829
Unrealized losses, 12 months or longer	(16,414)	(8,132)
Estimated fair value, Total	1,285,041	1,671,896
Unrealized losses, Total	(19,144)	(47,148)
Debt Securities | U.S. Treasury Bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	4,073	37,492
Unrealized losses, Less than 12 months	(11)	(685)
Estimated fair value, 12 months or longer	17,246
Unrealized losses, 12 months or longer	(210)
Estimated fair value, Total	21,319	37,492
Unrealized losses, Total	(221)	(685)
Debt Securities | Municipal Bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	48,817	230,180
Unrealized losses, Less than 12 months	(167)	(8,938)
Estimated fair value, 12 months or longer	105,820	27,687
Unrealized losses, 12 months or longer	(1,861)	(1,353)
Estimated fair value, Total	154,637	257,867
Unrealized losses, Total	(2,028)	(10,291)
Debt Securities | Foreign Bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	11,473	56,579
Unrealized losses, Less than 12 months	(63)	(626)
Estimated fair value, 12 months or longer	6,630
Unrealized losses, 12 months or longer	(72)
Estimated fair value, Total	18,103	56,579
Unrealized losses, Total	(135)	(626)
Debt Securities | Governmental Agency Bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	8,259	203,011
Unrealized losses, Less than 12 months	(25)	(5,375)
Estimated fair value, 12 months or longer	133,676	131
Unrealized losses, 12 months or longer	(2,684)	(26)
Estimated fair value, Total	141,935	203,142
Unrealized losses, Total	(2,709)	(5,401)
Debt Securities | Governmental Agency Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	424,099	838,411
Unrealized losses, Less than 12 months	(1,769)	(20,970)
Estimated fair value, 12 months or longer	402,830	124,425
Unrealized losses, 12 months or longer	(10,232)	(4,284)
Estimated fair value, Total	826,929	962,836
Unrealized losses, Total	(12,001)	(25,254)
Debt Securities | Non-Agency Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	1,871
Unrealized losses, Less than 12 months	(213)
Estimated fair value, 12 months or longer	6,566	12,086
Unrealized losses, 12 months or longer	(1,080)	(1,803)
Estimated fair value, Total	8,437	12,086
Unrealized losses, Total	(1,293)	(1,803)
Debt Securities | Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value, Less than 12 months	86,760	129,394
Unrealized losses, Less than 12 months	(482)	(2,422)
Estimated fair value, 12 months or longer	26,921	12,500
Unrealized losses, 12 months or longer	(275)	(666)
Estimated fair value, Total	113,681	141,894
Unrealized losses, Total	$ (757)	$ (3,088)