Available for Sale Securities (Detail) - USD ($) $ in Thousands	Apr. 01, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,980,186	$ 6,691,140
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	120,904	114,449
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	41,270	66,971
Fair Value	7,059,820	6,738,618
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,919,378	3,036,060
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4,964	2,211
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	9,748	24,649
Fair Value	2,914,594	3,013,622
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,616,734	2,469,192
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,530	1,359
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	28,113	33,903
Fair Value	2,590,151	2,436,648
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	164,548	164,548
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	463
Fair Value	164,548	164,085
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,279,526	1,021,340
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	114,410	110,879
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3,409	7,956
Fair Value	$ 1,390,527	$ 1,124,263