Short-term and Long-term Investments (Tables)

9 Months Ended

Sep. 30, 2014

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Investments

The following table summarizes the amortized cost, gross unrealized gains and losses and fair value of available-for-sale investments as of September 30, 2014:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Aggregate Fair Value
U.S. government debt securities	$	148,632	$	116	$	—	$	148,748
Certificates of deposit	1,020		—		—		1,020
Total	$	149,652	$	116	$	—	$	149,768

The following table summarizes the amortized cost, gross unrealized gains and losses and fair value of available-for-sale investments as of December 31, 2013:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Aggregate Fair Value
U.S. government debt securities	$	178,277	$	35	$	(13	)	$	178,299
Commercial paper	7,997		—		—			7,997
Certificates of deposit	2,266		—		(1		)	2,265
Total	$	188,540	$	35	$	(14	)	$	188,561

Summary of Estimated Fair Value of Available-for-Sale Investments Classified by Contractual Maturities

The estimated fair value of available-for-sale investments classified by their contractual maturities as of September 30, 2014 was as follows:

Due within one year	$	98,380
After one year through three years	51,388
Total	$	149,768