Financial Instruments FInancial Instruments (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	$ 45,527,000	$ 46,145,000
Assets, fair value	45,815,000
Deferred compensation plan	36,975,000	37,280,000
Liabilities, fair value	36,975,000	37,702,000
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	0	0
Assets, fair value	0
Deferred compensation plan	0	0
Liabilities, fair value	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	45,527,000	46,145,000
Assets, fair value	45,815,000
Deferred compensation plan	36,975,000	37,280,000
Liabilities, fair value	36,975,000	37,702,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	0	0
Assets, fair value	0
Deferred compensation plan	0	0
Liabilities, fair value	0	0
5 year interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative assets	180,000
Interest rate derivative liabilities		492,000
5 year interest rate swap | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative assets	0
Interest rate derivative liabilities		0
5 year interest rate swap | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative liabilities		492,000
5 year interest rate swap | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative assets	0
Interest rate derivative liabilities		0
10 year interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative assets	108,000
Interest rate derivative liabilities		(70,000)
10 year interest rate swap | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative assets	0
Interest rate derivative liabilities		0
10 year interest rate swap | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative liabilities		(70,000)
10 year interest rate swap | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate derivative assets	$ 0
Interest rate derivative liabilities		$ 0