Marketable Securities - (Tables)

9 Months Ended

Sep. 30, 2018

Schedule of Marketable Securities by Category

At September 30, 2018 and December 31, 2017, marketable securities are categorized as follows:

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
September 30, 2018
Municipal notes and bonds	$	70,092	$	—	$	87	$	70,005
Total marketable securities	$	70,092	$	—	$	87	$	70,005
December 31, 2017
Municipal notes and bonds	$	109,750	$	—	$	161	$	109,589
Total marketable securities	$	109,750	$	—	$	161	$	109,589

Schedule of Amortized Cost and Estimated Fair Value of Marketable Securities Classified by Maturity Date

The amortized cost and estimated fair value of marketable securities classified by the maturity date listed on the security, regardless of the Condensed Consolidated Balance Sheet classification, are as follows at September 30, 2018 and December 31, 2017:

	September 30, 2018				December 31, 2017
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	63,901	$	63,831	$	104,742	$	104,605
Due after one through five years		6,191		6,174		5,008		4,984
Due after five through ten years		—		—		—		—
Due after ten years		—		—		—		—
Total marketable securities	$	70,092	$	70,005	$	109,750	$	109,589

Summary of Estimated Fair Value and Gross Unrealized Holding Losses of Marketable Securities in Unrealized Loss Position

The following table summarizes the estimated fair value and gross unrealized holding losses of marketable securities, aggregated by investment instrument and period of time in an unrealized loss position, at September 30, 2018 and December 31, 2017:

	Unrealized Loss Position For Less Than 12 Months				Unrealized Loss Position For Greater Than 12 Months
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
September 30, 2018
Municipal notes and bonds	$	50,097	$	70	$	7,172	$	17
Total	$	50,097	$	70	$	7,172	$	17
December 31, 2017
Municipal notes and bonds	$	98,805	$	161	$	—	$	—
Total	$	98,805	$	161	$	—	$	—