Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following tables summarize significant assets and liabilities measured at fair value in the condensed consolidated balance sheets on a recurring basis for each of the fair value levels (in thousands):

	Fair Value Measurement at Reporting Date Using
March 31, 2018	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	4,891	$	—	$	—	$	4,891
Total assets	$	4,891	$	—	$	—	$	4,891
December 31, 2017
Cash equivalents
Money market funds	$	37,284	$	—	$	—	$	37,284
Commercial paper		9,967		—		—		9,967
Total assets	$	47,251	$	—	$	—	$	47,251
March 31, 2017
Cash equivalents
Money market funds	$	28,091	$	—	$	—	$	28,091
Total assets	$	28,091	$	—	$	—	$	28,091

Schedule of Carrying and Fair Value Amounts

The carrying values and estimated fair values of our financial instruments that are not required to be recorded at fair value in the condensed consolidated balance sheets were as follows:

		March 31, 2018				December 31, 2017				March 31, 2017
(in thousands)	Fair Value Hierarchy	Carrying Value		Fair Value		Carrying Value		Fair Value		Carrying Value		Fair Value
Assets:
Held-to-maturity marketable securities	Level 1	$	107,266	$	106,143	$	132,790	$	132,002	$	127,813	$	127,448
Liabilities (including current maturities):
2019 Notes1	Level 3	$	80,000	$	83,086	$	80,000	$	82,190	$	120,000	$	125,930
Credit Agreement - term loan1	Level 3		88,750		88,803		90,000		89,871		93,750		92,986
Credit Agreement - revolving  credit facility1	Level 3		55,000		54,858		55,000		55,054		30,000		29,520