Business Segments - Adjustments for Difference in Interim Medicare Part D Results for Segment Purposes and GAAP (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting [Abstract]
Benefit costs deferred	$ 21,279	$ 25,047
Government risk-sharing premium adjustment	(8,706)	(6,125)
Pre-tax addition to segment interim period income	12,573	18,922
After tax amount	$ 8,172	$ 12,299