OTHER ASSETS

Other assets at September 30, 2015 and December 31, 2014 consisted of the following (in thousands):



	September 30, 2015		December 31, 2014
Deferred debt issuance costs	$	34,827	$	27,204
Security deposits	14,168		12,368
Deferred tax assets	9,912		8,548
Investments	63,926		588
Other	18,426		8,640
Total	$	141,259	$	57,348

Deferred debt issuance costs arose from (i) the $1.0 billion aggregate principal amount of 1.0% Convertible Senior Notes, due March 15, 2018, issued in March 2012; (ii) the $1.0 billion aggregate principal amount of 0.35% Convertible Senior Notes, due June 15, 2020, issued in May 2013; (iii) the $1.0 billion aggregate principal amount of 0.9% Convertible Senior Notes, due September 15, 2021, issued in August 2014; (iv) the 1.0 billion Euro aggregate principal amount of 2.375% Senior Notes, due September 23, 2024, issued in September 2014; (v) the 1.0 billion Euro aggregate principal amount of 1.8% Senior Notes, due March 3, 2027, issued in March 2015, (vi) the $500 million aggregate principal amount of 3.65% Senior Notes, due March 15, 2025, issued in March 2015, and (vii) the $2.0 billion revolving credit facility entered into in June 2015. Included in the December 31, 2014 balance were debt issuance costs related to the $575.0 million aggregate principal amount of 1.25% Convertible Senior Notes, due March 15, 2015, issued in March 2010 and the $1.0 billion revolving credit facility entered into in October 2011. Deferred debt issuance costs are being amortized using the effective interest rate method and the period of amortization was determined at inception of the related debt agreements based upon the stated maturity dates. The termination of the revolving credit facility entered into in October 2011 resulted in a charge to interest expense of $1.0 million in June 2015 to write off the remaining unamortized debt issuance costs (see Note 8).

As of September 30, 2015, the Company held investments in equity securities of private companies of approximately $64 million, and these investments are accounted for under the cost method. As of September 30, 2015, the Company did not estimate the fair value of these cost-method investments because there were no identified events or changes in circumstances that may have a significant adverse impact on the carrying values of these investments.