Reserve for Known and Incurred but Not Reported Claims (Activity in Reserve for Known and Incurred but Not Reported Claims) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$ 1,025,863	$ 983,880
Provision related to current year	99,408	100,587
Provision related to prior years	2,980	6,511
Total Provision	102,388	107,098
Payments, net of recoveries, related to: Current year	30,610	30,230
Payments, net of recoveries, related to: Prior years	83,404	83,779
Total Payments, net of recoveries	114,014	114,009
Other	(772)	6,705
Balance at end of period	$ 1,013,465	$ 983,674