Available-for-Sale-Securitie

The following table is a summary of available-for-sale securities recorded in cash and cash equivalents in our Consolidated Balance Sheets (in thousands):



	December 31, 2016								December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Certificate of deposits	$	—	$	—	$	—	$	—	$	249.0	$	—	$	—	$	249.0
Corporate debt securities	—		—		—		—		1,047.2		—		—		1,047.2
Money market funds	4,426.8		—		—		4,426.8		837.7		—		—		837.7
Municipal debt securities	—		—		—		—		4,740.9		0.8		—		4,741.7
Total	$	4,426.8	$	—	$	—	$	4,426.8	$	6,874.8	$	0.8	$	—	$	6,875.6

Estimated fair values of available-for-sale securities are generally based on prices obtained from commercial pricing services. The following table summarizes the classification of the available-for-sale debt securities on our Consolidated Balance Sheets (in thousands):



	December 31, 2016		December 31, 2015
Cash and cash equivalents	$	4,426.8	$	6,875.6
Marketable securities	—		—
Total	$	4,426.8	$	6,875.6

The following table summarizes our portfolio of available-for-sale debt securities by contractual maturity (in thousands):



	December 31, 2016
	Amortized Cost		Estimated Fair Value
Less than one year	$	4,426.8	$	4,426.8
Greater than one year	—		—
Total	$	4,426.8	$	4,426.8