Cash, Cash Equivalents and Investments - Summary of Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 336,806
Gross Unrealized Gains	1,004
Gross Unrealized Losses	(321)
Fair Value, Total	337,489
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	146,073
Corporate Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,965
Gross Unrealized Gains	68
Gross Unrealized Losses	(32)
Fair Value, Total	46,001
Corporate Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,464
Gross Unrealized Gains	647
Gross Unrealized Losses	(39)
Fair Value, Total	100,072
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	52,376
Asset-Backed Securities [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,668
Gross Unrealized Gains	16
Gross Unrealized Losses	(18)
Fair Value, Total	17,666
Asset-Backed Securities [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,831
Gross Unrealized Gains	32
Gross Unrealized Losses	(153)
Fair Value, Total	34,710
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	34,070
Municipal Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,198
Gross Unrealized Gains	26
Fair Value, Total	16,224
Municipal Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,726
Gross Unrealized Gains	121
Gross Unrealized Losses	(1)
Fair Value, Total	17,846
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	36,923
Agency Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,489
Gross Unrealized Losses	(7)
Fair Value, Total	7,482
Agency Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,411
Gross Unrealized Gains	54
Gross Unrealized Losses	(24)
Fair Value, Total	29,441
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	42,273
Treasury Bills [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,996
Gross Unrealized Gains	1
Fair Value, Total	5,997
Treasury Bills [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	36,277
Gross Unrealized Gains	8
Gross Unrealized Losses	(9)
Fair Value, Total	36,276
Covered Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	11,182
Covered Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,637
Gross Unrealized Gains	2
Gross Unrealized Losses	(21)
Fair Value, Total	5,618
Covered Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,555
Gross Unrealized Gains	9
Fair Value, Total	5,564
Sovereign Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	14,592
Sovereign Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,000
Gross Unrealized Losses	(14)
Fair Value, Total	3,986
Sovereign Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,589
Gross Unrealized Gains	20
Gross Unrealized Losses	(3)
Fair Value, Total	$ 10,606