Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value of Assets and Liabilities Measured on Recurring Basis

The following tables provide the assets carried at fair value and measured on a recurring basis:

			Fair Value Measurements at Reporting Date Using:
(in thousands)	December 31, 2017		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents	$	312,914	$	312,914	$	—	$	—
Short-term investments	$	286	$	—	$	286	$	—
Deferred compensation plan investments	$	3,742	$	3,742	$	—	$	—

			Fair Value Measurements at Reporting Date Using:
(in thousands)	December 31, 2016		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents	$	333,975	$	333,975	$	—	$	—
Short-term investments	$	381	$	—	$	381	$	—
Deferred compensation plan investments	$	459	$	459	$	—	$	—