4. Cash, Cash Equivalents, and Marketable Securities

Cash, cash equivalents, and marketable securities consisted of the following at September 30, 2015 and December 31, 2014 (in thousands):



	September 30, 2015		December 31, 2014
Cash and cash equivalents:
Cash	$	1,103,684	$	1,480,452
Cash equivalents:
Money market funds	86,019		1,602
Total cash and cash equivalents	1,189,703		1,482,054
Marketable securities:
Foreign debt	579,814		462,731
Time deposits	40,000		40,000
U.S. debt	—		2,800
U.S. government obligations	—		3,501
Total marketable securities	619,814		509,032
Total cash, cash equivalents, and marketable securities	$	1,809,517	$	1,991,086

We classify our marketable securities as available-for-sale. Accordingly, we record them at fair value and account for the net unrealized gains and losses as part of “Accumulated other comprehensive income” until realized. We record realized gains and losses on the sale or maturity of our marketable securities in “Other expense, net” computed using the specific identification method.

During the three and nine months ended September 30, 2015 we realized no gains or losses on the sale or maturity of our marketable securities. During the three and nine months ended September 30, 2014, we realized zero and $0.2 million of gains on the sale or maturity of our marketable securities. See Note 8. “Fair Value Measurements” to our condensed consolidated financial statements for information about the fair value of our marketable securities.

As of September 30, 2015, we identified two investments totaling $26.6 million that had been in a loss position for a period of time greater than 12 months with unrealized losses of $0.1 million. As of December 31, 2014, we identified two investments totaling $41.1 million that had been in a loss position for a period of time greater than 12 months with unrealized losses of less than $0.1 million. The unrealized losses were primarily due to increases in interest rates relative to rates at the time of purchase. Based on the underlying credit quality of the investments, we do not intend to sell these securities prior to the recovery of our cost basis. Therefore, we did not consider these securities to be other-than-temporarily impaired. All of our available-for-sale marketable securities are subject to a periodic impairment review. We did not identify any of our marketable securities as other-than-temporarily impaired as of September 30, 2015 and December 31, 2014.

The following tables summarize the unrealized gains and losses related to our available-for-sale marketable securities, by major security type, as of September 30, 2015 and December 31, 2014 (in thousands):



	As of September 30, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Foreign debt	$	580,282	$	224	$	692	$	579,814
Time deposits	40,000		—		—		40,000
Total	$	620,282	$	224	$	692	$	619,814



	As of December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Foreign debt	$	463,466	$	18	$	753	$	462,731
Time deposits	40,000		—		—		40,000
U.S. debt	2,800		—		—		2,800
U.S. government obligations	3,500		1		—		3,501
Total	$	509,766	$	19	$	753	$	509,032

The contractual maturities of our marketable securities as of September 30, 2015 and December 31, 2014 were as follows (in thousands):



	As of September 30, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
One year or less	$	240,447	$	15	$	216	$	240,246
One year to two years	271,445		29		439		271,035
Two years to three years	108,390		180		37		108,533
Total	$	620,282	$	224	$	692	$	619,814



	As of December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
One year or less	$	329,974	$	14	$	174	$	329,814
One year to two years	125,892		5		380		125,517
Two years to three years	53,900		—		199		53,701
Total	$	509,766	$	19	$	753	$	509,032

The net unrealized losses of $0.5 million and $0.7 million as of September 30, 2015 and December 31, 2014, respectively, on our marketable securities were primarily the result of increases in interest rates relative to rates at the time of purchase. Our investment policy requires marketable securities to be highly rated and limits the security types, issuer concentration, and duration to maturity of our marketable securities portfolio.

The following tables show gross unrealized losses and estimated fair values for those marketable securities that were in an unrealized loss position as of September 30, 2015 and December 31, 2014, aggregated by major security type and the length of time the marketable securities have been in a continuous loss position (in thousands):



	As of September 30, 2015
	In Loss Position for Less Than 12 Months				In Loss Position for 12 Months or Greater				Total
	Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses
Foreign debt	$	359,106	$	588	$	26,594	$	104	$	385,700	$	692
Total	$	359,106	$	588	$	26,594	$	104	$	385,700	$	692



	As of December 31, 2014
	In Loss Position for Less Than 12 Months				In Loss Position for 12 Months or Greater				Total
	Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses
Foreign debt	$	391,840	$	740	$	41,060	$	13	$	432,900	$	753
Total	$	391,840	$	740	$	41,060	$	13	$	432,900	$	753