Investments (Tables)

6 Months Ended

Jun. 30, 2015

Investments, Debt and Equity Securities [Abstract]

Schedule of Investments

At June 30, 2015 investments classified as available-for-sale securities were as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Debt securities:
Commercial paper (1)	$	256,685	$	154	$	—	$	256,839
U.S. Treasury securities	259,538		84		—		259,622
Corporate debt securities	102,366		1,547		—		103,913
Preferred stock	11,858		124		—		11,982
	$	630,447	$	1,909	$	—	$	632,356

(1) Recorded in Cash and cash equivalents on the Company’s Condensed Consolidated Balance Sheets.

At December 31, 2014 investments classified as available-for-sale securities were as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Debt securities:
U.S. Treasury securities	$	509,783	$	32	$	—	$	509,815
Corporate debt securities	101,587		—		1,482		100,105
Preferred stock	26,963		—		5		26,958
	$	638,333	$	32	$	1,487	$	636,878

Continuous Unrealized Loss Position

The Company has revised this disclosure in the following table that provides the corporate debt securities continuous unrealized loss position and its related fair values:    

	As of June 30, 2015				As of December 31, 2014
	Less Than 12 Months		12 Months or Greater		Less Than 12 Months		12 Months or Greater
	Fair Value	Unrealized Losses	Fair Value	Unrealized Losses	Fair Value	Unrealized Losses	Fair Value	Unrealized Losses
Corporate debt securities	—	—	—	—	85,845	1,294	14,260	188

Contractual Maturities of Investments

The net carrying value and estimated fair value of investments classified as available-for-sale at June 30, 2015, by contractual maturity are shown in the following table. Actual maturities may differ from contractual maturities because certain borrowers have the right to call or prepay obligations.

	Amortized Cost		Fair Value
Due in one year or less	$	516,223	$	516,461
Due after one year through five years	102,366		103,913
	618,589		620,374
Preferred stock	11,858		11,982
	$	630,447	$	632,356