Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Apr. 01, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 3,509,726	$ 4,507,220
Less Than 12 Months, Unrealized Losses	37,954	62,157
12 Months or Longer, Fair Value	79,846	96,009
12 Months or Longer, Unrealized Losses	3,316	4,814
Total, Fair Value	3,589,572	4,603,229
Total, Unrealized Losses	41,270	66,971
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	1,304,761	2,360,143
Less Than 12 Months, Unrealized Losses	8,696	24,416
12 Months or Longer, Fair Value	23,986	6,099
12 Months or Longer, Unrealized Losses	1,052	233
Total, Fair Value	1,328,747	2,366,242
Total, Unrealized Losses	9,748	24,649
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	2,041,367	1,921,367
Less Than 12 Months, Unrealized Losses	27,645	33,354
12 Months or Longer, Fair Value	51,806	51,769
12 Months or Longer, Unrealized Losses	468	549
Total, Fair Value	2,093,173	1,973,136
Total, Unrealized Losses	28,113	33,903
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	0	164,085
Less Than 12 Months, Unrealized Losses	0	463
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	0	164,085
Total, Unrealized Losses	0	463
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	163,598	61,625
Less Than 12 Months, Unrealized Losses	1,613	3,924
12 Months or Longer, Fair Value	4,054	38,141
12 Months or Longer, Unrealized Losses	1,796	4,032
Total, Fair Value	167,652	99,766
Total, Unrealized Losses	$ 3,409	$ 7,956