Adjustments for Difference in Interim Medicare Part D Results for Segment Purposes and GAAP (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Segment Reporting [Abstract]
Benefit costs deferred	$ 29,945		$ 32,640
Government risk-sharing premium adjustment	(14,895)		(11,274)
Pre-tax addition to segment interim period income	15,050	[1]	21,366	[2]
After tax amount	$ 9,782		$ 13,888

[1] Elimination of intersegment commission.

[2] Medicare Part D items adjusted to GAAP from the segment analysis, which matches expected benefits with policy premium.