Stock Options Granted, Forfeited, Exercised and Expired (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding at beginning of period				1,765,881
Number of Shares, Granted	0		0	156,500		159,500
Number of Shares, Forfeited				(6,667)
Number of Shares, Exercised	(93,911)		(42,780)	(197,965)		(103,310)
Number of Shares, Expired				(1,734)
Number of Shares, Outstanding at end of period	1,716,015			1,716,015
Number of Shares, Exercisable at end of period	1,358,175			1,358,175
Weighted Average Exercise Price, Outstanding at beginning of period				$ 79.24
Weighted Average Exercise Price, Granted				$ 75.16
Weighted Average Exercise Price, Forfeited				$ 90.45
Weighted Average Exercise Price, Exercised				$ 40.87
Weighted Average Exercise Price, Expired				$ 17.25
Weighted Average Exercise Price, Outstanding at end of period	$ 83.31			$ 83.31
Weighted Average Exercise Price, Exercisable at end of period	$ 83.12			$ 83.12
Aggregate Exercise Price, Outstanding at beginning of period				$ 139,922
Aggregate Exercise Price, Granted	11,763			11,763
Aggregate Exercise Price, Forfeited				(603)
Aggregate Exercise Price, Exercised				(8,091)
Aggregate Exercise Price, Expired				(30)
Aggregate Exercise Price, Outstanding at end of period	142,961			142,961
Aggregate Exercise Price, Exercisable at end of period	112,887			112,887
Weighted Average Remaining Contractual Term, Outstanding at end of period, years				3 years 6 months
Weighted Average Remaining Contractual Term, Exercisable at end of period, years				2 years 329 days
Aggregate Intrinsic Value, Outstanding at end of period	5,875	[1]		5,875	[1]
Aggregate Intrinsic Value, Exercisable at end of period	$ 5,875	[1]		$ 5,875	[1]

[1] The aggregate intrinsic value of the stock options was calculated by identifying those stock options that had a lower exercise price than the closing market price of our common stock on June 29, 2012 and multiplying the difference between the closing market price of our common stock and the exercise price of each of those stock options by the number of shares subject to those stock options that were outstanding or exercisable, as applicable.