Supplemental Financial Statement Information (Tables)

3 Months Ended

Mar. 31, 2019

Balance Sheet Components Disclosure [Abstract]

Summary of Cash Equivalents and Short-Term Investments

The following tables summarize the cost or amortized cost, gross unrealized gain, gross unrealized loss and fair value of the Company’s cash equivalents and short-term investments as of the dates indicated (in thousands):

	March 31, 2019
	Cost or Amortized		Unrealized					Estimated Fair
	Cost		Gains		Losses			Value
Unrestricted Balances (1)
Money market funds	$	1,406	$	—	$	—		$	1,406
Certificates of deposit		168,700		203		—			168,903
Commercial paper		441,803		190		(32	)		441,961
Corporate bonds		94,415		93		(1	)		94,507
Total unrestricted cash equivalents and short-term investments		706,324		486		(33	)		706,777
Restricted Balances (2)(3)
Money market funds		2,822		—		—			2,822
Certificates of deposit		348,007		364		(2	)		348,369
Commercial paper		696,251		176		(90	)		696,337
Corporate bonds		62,204		58		(8	)		62,254
Total restricted cash equivalents and investments		1,109,284		598		(100	)		1,109,782
Total unrestricted and restricted cash equivalents and investments	$	1,815,608	$	1,084	$	(133	)	$	1,816,559

(1) Included in cash and cash equivalents and short-term investments in the Company’s condensed consolidated balance sheet as of March 31, 2019 in addition to $328.1 million of cash.

(2) Included in restricted cash and cash equivalents and restricted investments in the Company’s condensed consolidated balance sheet as of March 31, 2019 in addition to $58.0 million of restricted cash.

(3) Included in prepaid expenses and other current assets in the Company’s condensed consolidated balance sheet as of March 31, 2019 is $1.9 million of restricted cash.

	December 31, 2018
	Cost or Amortized		Unrealized					Estimated Fair
	Cost		Gains		Losses			Value
Unrestricted Balances (1)
Money market funds	$	38,528	$	—	$	—		$	38,528
Certificates of deposit		497,748		19		(213	)		497,554
Commercial paper		1,135,092		38		(409	)		1,134,721
Corporate bonds		119,043		19		(23	)		119,039
Total unrestricted cash equivalents and short-term investments		1,790,411		76		(645	)		1,789,842
Restricted Balances (2)(3)
Money market funds		4,620		—		—			4,620
Certificates of deposit		307,650		41		(87	)		307,604
Commercial paper		624,719		17		(227	)		624,509
Corporate bonds		65,616		6		(36	)		65,586
Total restricted cash equivalents and investments		1,002,605		64		(350	)		1,002,319
Total unrestricted and restricted cash equivalents and investments	$	2,793,016	$	140	$	(995	)	$	2,792,161

(1) Included in cash and cash equivalents and short-term investments in the Company’s condensed consolidated balance sheet as of December 31, 2018 in addition to $248.0 million of cash.

(2) Included in restricted cash and cash equivalents and restricted investments in the Company’s condensed consolidated balance sheet as of December 31, 2018 in addition to $50.2 million of restricted cash.

(3) Included in prepaid expenses and other current assets in the Company’s condensed consolidated balance sheet as of December 31, 2018 is $1.4 million of restricted cash.

Summary of Rollforward of the Insurance Reserve

The following table provides a rollforward of the insurance reserve for the periods presented (in thousands):

	Three Months Ended March 31,
	2019			2018
Beginning balance	$	810,273		$	376,538
Losses paid		(99,551	)		(48,855	)
Change in estimates		23,820			3,392
Reserves for current period		202,442			135,193
Ending balance	$	936,984		$	466,268