Guarantees and Contingencies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
New Tricare South Region Contract
Loss Contingencies [Line Items]
Contract term, years	5 years
Contract expiration date	Mar. 31, 2017
Military services
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	1.00%
Total Medicare
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	72.00%
Medicaid
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	4.00%