Debt And Equity Securities (Amortized Cost And Estimated Fair Value Of Debt Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value	$ 2,651,881	$ 2,201,911
U.S. Treasury Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	6,140
Estimated fair value	6,257
Amortized cost	49,848
Estimated fair value	50,952
Amortized cost	21,370
Estimated fair value	21,606
Amortized cost	3,293
Estimated fair value	3,360
Amortized Cost	80,651
Estimated fair value	82,175
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,445
Estimated fair value	2,459
Amortized cost	89,689
Estimated fair value	91,428
Amortized cost	122,993
Estimated fair value	129,286
Amortized cost	146,785
Estimated fair value	152,649
Amortized Cost	361,912
Estimated fair value	375,822
Foreign Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	41,991
Estimated fair value	42,189
Amortized cost	181,304
Estimated fair value	183,069
Amortized cost	13,335
Estimated fair value	13,487
Amortized Cost	236,630
Estimated fair value	238,745
Governmental Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	106
Estimated fair value	106
Amortized cost	124,134
Estimated fair value	124,803
Amortized cost	176,996
Estimated fair value	177,705
Amortized cost	23,087
Estimated fair value	22,836
Amortized Cost	324,323
Estimated fair value	325,450
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,305
Estimated fair value	7,345
Amortized cost	152,501
Estimated fair value	156,665
Amortized cost	139,827
Estimated fair value	148,980
Amortized cost	12,062
Estimated fair value	13,321
Amortized Cost	311,695
Estimated fair value	326,311
Total Debt Securities Excluding Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	57,987
Estimated fair value	58,356
Amortized cost	597,476
Estimated fair value	606,917
Amortized cost	474,521
Estimated fair value	491,064
Amortized cost	185,227
Estimated fair value	192,166
Amortized Cost	1,315,211
Estimated fair value	1,348,503
Total Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,298,064
Estimated fair value	1,303,378
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,613,275
Estimated fair value	$ 2,651,881