Financial Instruments and Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2015

Fair Value Disclosures [Abstract]

Schedule of Financial Instruments Measured at Fair Value on a Recurring Basis

The financial instruments measured at fair value on a recurring basis at June 30, 2015 were as follows:

	Level 1		Level 2		Level 3		Total Fair Value
Cash equivalents:
Money market funds	$	39,637	$	—	$	—	$	39,637
Commercial paper	256,839		—		—		256,839
Debt securities:
U.S. Treasury securities	259,622		—		—		259,622
Corporate debt securities	—		103,913		—		103,913
Preferred stock	—		11,982		—		11,982
Restricted investments:
Guaranteed income fund	—		7,129		—		7,129
	$	556,098	$	123,024	$	—	$	679,122

The financial instruments measured at fair value on a recurring basis at December 31, 2014 were as follows:

	Level 1		Level 2		Level 3		Total Fair Value
Cash equivalents:
Money market funds	$	19,971	$	—	$	—	$	19,971
Debt securities:
U.S. Treasury securities	509,815		—		—		509,815
Corporate debt securities	—		100,105		—		100,105
Preferred stock	—		26,958		—		26,958
Restricted investments:
Guaranteed income fund	—		7,940		—		7,940
	$	529,786	$	135,003	$	—	$	664,789

Carrying Amount and Fair Value of Financial Instruments

The carrying amount and fair value of the Company’s financial instruments were as follows:

	June 30, 2015					December 31, 2014
	Carrying  value		Fair value		Level	Carrying  value		Fair value		Level
Assets
Pledged treasury securities	$	25,360	$	25,494	1	$	25,670	$	26,501	1
Retained interest investments	$	10,078	$	13,116	3	$	9,932	$	13,026	3
Investments held by special purpose entities (Note 5)	$	209,459	$	209,308	3	$	209,857	$	209,679	3
Liabilities
Senior Notes held by special purpose entity (Note 5)	$	177,392	$	177,982	3	$	177,341	$	177,940	3