Available-for-Sale-Securities (Tables)

12 Months Ended

Dec. 31, 2017

Available-for-sale Securities [Abstract]

Schedule of Available-for-sale Securities Reconciliation [Table Text Block]

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, 2017									December 31, 2016
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Corporate debt securities	$	42,701.0	$	—	$	(28.0	)	$	42,673.0	$	—	$	—	$	—	$	—
Money market funds	9,211.5		—		—			9,211.5		4,426.8		—		—		4,426.8
Total	$	51,912.5	$	—	$	(28.0	)	$	51,884.5	$	4,426.8	$	—	$	—	$	4,426.8

Marketable Securities [Table Text Block]

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, 2017		December 31, 2016
Cash and cash equivalents	$	25,967.8	$	4,426.8
Marketable securities	25,916.7		—
Total	$	51,884.5	$	4,426.8

Investments Classified by Contractual Maturity Date [Table Text Block]

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

	December 31, 2017
	Amortized Cost		Estimated Fair Value
Less than one year	$	51,912.5	$	51,884.5
Greater than one year	—		—
Total	$	51,912.5	$	51,884.5