Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]

Fair value assets and liabilities measured on recurring basis

The following table provides a summary of the Company’s significant financial assets and liabilities carried at fair value and measured on a recurring basis (in thousands):

			Fair Value Measurements at December 31, 2017
	Carrying Value at December 31, 2017		Quoted Prices in Active Markets (Level 1)		Significant Other Observable  Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Restricted investments:
Rabbi Trust	$	20,763	$	—	$	20,763	$	—
Fixed income securities	1,902		—		1,902		—
Liabilities:
Interest rate swap derivatives	$	13,992	$	—	$	13,992	$	—

			Fair Value Measurements at December 31, 2016
	Carrying Value at December 31, 2016		Quoted Prices in Active Markets (Level 1)		Significant Other Observable  Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Restricted investments:
Rabbi Trust	$	15,662	$	—	$	15,662	$	—
Fixed income securities	1,782		—		1,782		—
Liabilities:
Interest rate swap derivatives	$	18,679	$	—	$	18,679	$	—