Fair Value Measurements - Schedule of Fair Value Hierarchy of Financial Assets Carried at Fair Value and Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	$ 215,609	$ 203,480
Available-for-sale Securities, Equity Securities, Fair Value	4,591
Total available-for-sale securities	220,200
Fair value measurements, Recurring
Cash equivalents:
Total cash equivalents	27,339	55,504
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	215,609
Available-for-sale Securities, Equity Securities, Fair Value	4,591
Total available-for-sale securities	220,200	203,480
Total assets at fair value	247,539	258,984
Fair value measurements, Recurring | Foreign Government Debt Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	6,619
Fair value measurements, Recurring | US Government Agencies Debt Securities
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	84,693	58,114
Fair value measurements, Recurring | Commercial paper
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	18,092	14,496
Fair value measurements, Recurring | Time deposits
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	29,618	9,880
Fair value measurements, Recurring | Corporate Bond Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	1,533
Fair value measurements, Recurring | Taxable municipal bonds
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	75,054	120,990
Fair value measurements, Recurring | Corporate Bond Securities [Member]
Cash equivalents:
Total cash equivalents	1,206
Fair value measurements, Recurring | US Government Agencies Debt Securities
Cash equivalents:
Total cash equivalents		6,400
Fair value measurements, Recurring | Money market and other funds
Cash equivalents:
Total cash equivalents	14,012	9,391
Fair value measurements, Recurring | Commercial paper
Cash equivalents:
Total cash equivalents	5,200	17,999
Fair value measurements, Recurring | Time deposits
Cash equivalents:
Total cash equivalents	1,246	499
Fair value measurements, Recurring | Taxable municipal bonds
Cash equivalents:
Total cash equivalents	5,675	21,215
Fair value measurements, Recurring | Fair Value, Inputs, Level 1
Cash equivalents:
Total cash equivalents	0	0
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0
Available-for-sale Securities, Equity Securities, Fair Value	4,591
Total available-for-sale securities	4,591	0
Total assets at fair value	4,591	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Foreign Government Debt Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | US Government Agencies Debt Securities
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Commercial paper
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Time deposits
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Corporate Bond Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Taxable municipal bonds
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Corporate Bond Securities [Member]
Cash equivalents:
Total cash equivalents	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | US Government Agencies Debt Securities
Cash equivalents:
Total cash equivalents		0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Money market and other funds
Cash equivalents:
Total cash equivalents	0	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Commercial paper
Cash equivalents:
Total cash equivalents	0	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Time deposits
Cash equivalents:
Total cash equivalents	0	0
Fair value measurements, Recurring | Fair Value, Inputs, Level 1 | Taxable municipal bonds
Cash equivalents:
Total cash equivalents	0	0
Fair value measurements, Recurring | Significant other observable inputs (Level 2)
Cash equivalents:
Total cash equivalents	27,339	55,504
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	215,609
Available-for-sale Securities, Equity Securities, Fair Value	0
Total available-for-sale securities	215,609	203,480
Total assets at fair value	242,948	258,984
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Foreign Government Debt Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	6,619
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | US Government Agencies Debt Securities
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	84,693	58,114
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Commercial paper
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	18,092	14,496
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Time deposits
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	29,618	9,880
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Corporate Bond Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	1,533
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Taxable municipal bonds
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	75,054	120,990
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Corporate Bond Securities [Member]
Cash equivalents:
Total cash equivalents	1,206
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | US Government Agencies Debt Securities
Cash equivalents:
Total cash equivalents		6,400
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Money market and other funds
Cash equivalents:
Total cash equivalents	14,012	9,391
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Commercial paper
Cash equivalents:
Total cash equivalents	5,200	17,999
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Time deposits
Cash equivalents:
Total cash equivalents	1,246	499
Fair value measurements, Recurring | Significant other observable inputs (Level 2) | Taxable municipal bonds
Cash equivalents:
Total cash equivalents	5,675	21,215
Fair value measurements, Recurring | Significant unobservable inputs (Level 3)
Cash equivalents:
Total cash equivalents	0	0
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0
Available-for-sale Securities, Equity Securities, Fair Value	0
Total available-for-sale securities	0	0
Total assets at fair value	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Foreign Government Debt Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | US Government Agencies Debt Securities
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Commercial paper
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Time deposits
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Corporate Bond Securities [Member]
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Taxable municipal bonds
Available-for-sale securities:
Available-for-sale Securities, Debt Securities, Fair Value	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Corporate Bond Securities [Member]
Cash equivalents:
Total cash equivalents	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | US Government Agencies Debt Securities
Cash equivalents:
Total cash equivalents		0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Money market and other funds
Cash equivalents:
Total cash equivalents	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Commercial paper
Cash equivalents:
Total cash equivalents	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Time deposits
Cash equivalents:
Total cash equivalents	0	0
Fair value measurements, Recurring | Significant unobservable inputs (Level 3) | Taxable municipal bonds
Cash equivalents:
Total cash equivalents	$ 0	$ 0