Summary of Company's Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 807,843	$ 297,323
Gross Unrealized Gains	28	66
Gross Unrealized Losses	(1,121)	(86)
Fair Value	806,750	297,303
Certificates of deposit (Due within 1 year)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,300
Fair Value	24,300
Commercial paper (Due within 1 year)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,785	11,983
Gross Unrealized Gains	11
Gross Unrealized Losses		(5)
Fair Value	40,796	11,978
Corporate notes (Due within 1 year)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	449,044	154,175
Gross Unrealized Gains	14	33
Gross Unrealized Losses	(293)	(46)
Fair Value	448,765	154,162
Corporate notes (Due after 1 year through 2 years)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	214,510	74,312
Gross Unrealized Gains		23
Gross Unrealized Losses	(730)	(35)
Fair Value	213,780	74,300
Municipal debt securities (Due after 1 year through 2 years)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,002
Gross Unrealized Gains	3
Fair Value	9,005
U.S. government-sponsored enterprise securities (Due within 1 year)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,069	26,553
Gross Unrealized Gains		8
Gross Unrealized Losses	(1)
Fair Value	13,068	26,561
U.S. government-sponsored enterprise securities (Due after 1 year through 2 years)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	51,879	30,300
Gross Unrealized Gains		2
Gross Unrealized Losses	(91)
Fair Value	51,788	30,302
U.S. treasury securities (Due after 1 year through 2 years)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,254
Gross Unrealized Losses	(6)
Fair Value	$ 5,248

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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