INVESTMENTS - Components of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	$ 92,835	$ 67,983
Unrealized Gains	3	3
Unrealized Losses	(51)	(13)
Fair Value	92,787	67,973
Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	90,947	65,296
Unrealized Gains	3	3
Unrealized Losses	(51)	(13)
Fair Value	90,899	65,286
Investments [Member] | Money Market Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	32,721	29,816
Unrealized Gains
Unrealized Losses
Fair Value	32,721	29,816
Investments [Member] | Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	25,740	5,494
Unrealized Gains	2	1
Unrealized Losses	(6)	(2)
Fair Value	25,736	5,493
Investments [Member] | Corporate Bonds and Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	32,486	29,986
Unrealized Gains	1	2
Unrealized Losses	(45)	(11)
Fair Value	32,442	29,977
Deferred Compensation Plan Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	1,888	2,687
Unrealized Gains
Unrealized Losses
Fair Value	$ 1,888	$ 2,687