Cash Equivalent and Investments (Parenthetical) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Minimum [Member] | Certificates Of Deposit [Member] | Short Term Investments [Member]
Schedule Of Investments [Line Items]
Securities Maturity period	1 month	1 month
Minimum [Member] | Certificates Of Deposit [Member] | Other Assets [Member]
Schedule Of Investments [Line Items]
Securities Maturity period	1 month	1 month
Minimum [Member] | Fixed Maturity and Mutual Funds [Member]
Schedule Of Investments [Line Items]
Securities Maturity period	2 months	11 months
Maximum [Member] | Certificates Of Deposit [Member] | Short Term Investments [Member]
Schedule Of Investments [Line Items]
Securities Maturity period	12 months	12 months
Maximum [Member] | Certificates Of Deposit [Member] | Cash And Cash Equivalents [Member]
Schedule Of Investments [Line Items]
Securities Maturity period	90 days
Maximum [Member] | Certificates Of Deposit [Member] | Other Assets [Member]
Schedule Of Investments [Line Items]
Securities Maturity period	18 months	27 months
Maximum [Member] | Fixed Maturity and Mutual Funds [Member]
Schedule Of Investments [Line Items]
Securities Maturity period	22 months	31 months