Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurements, Nonrecurring [Table Text Block]

	Fair Value Measurement at December 31, 2017
	Total			Level 1		Level 2			Level 3
Assets:
Deferred compensation assets (1)	$	46,145		$	—	$	46,145		$	—
Liabilities:
Deferred compensation plan	$	37,280		$	—	$	37,280		$	—
5 year interest rate swap	(70		)	—		(70		)	—
10 year interest rate swap	492			—		492			—
	$	37,702		$	—	$	37,702		$	—

	Fair Value Measurement at December 31, 2016
	Total		Level 1		Level 2		Level 3
Assets:
Deferred compensation assets (1)	$	38,905	$	—	$	38,905	$	—
Liabilities:
Deferred compensation plan	$	31,672	$	—	$	31,672	$	—
5 year interest rate swap	211		—		211		—
10 year interest rate swap	835		—		835		—
	$	32,718	$	—	$	32,718	$	—
(1) Deferred compensation assets consist of the cash surrender value of life insurance policies and are intended to assist in the funding of the deferred compensation arrangements.