Fair Value Measurements - Schedule of Fair Value Hierarchy of Financial Assets and Liabilities Carried at Fair Value and Measured on Recurring Basis (Detail) - Fair value measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Cash equivalents:
Total cash equivalents		$ 14,318
Debt securities:
Available-for-sale debt securities		251,620
Total assets	$ 16,711	265,938
Total liabilities at fair value	2,951
Contingent consideration liability [Member]
Debt securities:
Total liabilities at fair value	2,951
U.S. government securities [Member]
Debt securities:
Available-for-sale debt securities	11,301	100,818
Money market and other funds [Member]
Cash equivalents:
Total cash equivalents	5,410	8,322
International government securities [Member]
Debt securities:
Available-for-sale debt securities		6,560
Commercial paper [Member]
Debt securities:
Available-for-sale debt securities		24,589
Time deposits [Member]
Cash equivalents:
Total cash equivalents		1,242
Debt securities:
Available-for-sale debt securities		30,759
Corporate bonds [Member]
Debt securities:
Available-for-sale debt securities		1,528
Taxable municipal bonds [Member]
Cash equivalents:
Total cash equivalents		4,754
Debt securities:
Available-for-sale debt securities		87,366
Quoted prices in active markets using identical assets (Level 1) [Member]
Debt securities:
Total liabilities at fair value	0
Quoted prices in active markets using identical assets (Level 1) [Member] | Contingent consideration liability [Member]
Debt securities:
Total liabilities at fair value	0
Significant other observable inputs (Level 2) [Member]
Cash equivalents:
Total cash equivalents		14,318
Debt securities:
Available-for-sale debt securities		251,620
Total assets	16,711	265,938
Total liabilities at fair value	0
Significant other observable inputs (Level 2) [Member] | Contingent consideration liability [Member]
Debt securities:
Total liabilities at fair value	0
Significant other observable inputs (Level 2) [Member] | U.S. government securities [Member]
Debt securities:
Available-for-sale debt securities	11,301	100,818
Significant other observable inputs (Level 2) [Member] | Money market and other funds [Member]
Cash equivalents:
Total cash equivalents	5,410	8,322
Significant other observable inputs (Level 2) [Member] | International government securities [Member]
Debt securities:
Available-for-sale debt securities		6,560
Significant other observable inputs (Level 2) [Member] | Commercial paper [Member]
Debt securities:
Available-for-sale debt securities		24,589
Significant other observable inputs (Level 2) [Member] | Time deposits [Member]
Cash equivalents:
Total cash equivalents		1,242
Debt securities:
Available-for-sale debt securities		30,759
Significant other observable inputs (Level 2) [Member] | Corporate bonds [Member]
Debt securities:
Available-for-sale debt securities		1,528
Significant other observable inputs (Level 2) [Member] | Taxable municipal bonds [Member]
Cash equivalents:
Total cash equivalents		4,754
Debt securities:
Available-for-sale debt securities		$ 87,366
Significant unobservable inputs (Level 3) [Member]
Debt securities:
Total liabilities at fair value	2,951
Significant unobservable inputs (Level 3) [Member] | Contingent consideration liability [Member]
Debt securities:
Total liabilities at fair value	$ 2,951