Fair Value (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Summary of changes in fair value of marketable securities [Roll Forward]
Balance, beginning of period	$ 26,280,000	$ 23,172,000
Actual return on plan assets: [Abstract]
Relating to assets still held at the reporting date	(1,597,000)	1,249,000
Purchases and issuances	3,025,000	2,798,000
Sales and settlements	(416,000)	(939,000)
Transfers into Level 3	0	0
Balance, End of period	27,292,000	26,280,000
Fair Value on a Recurring Basis [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	47,121,000	86,574,000
Forward contracts	485,000	1,661,000
Insurance company contracts	27,292,000	26,280,000
Total	74,898,000	114,515,000
Restricted current investments	14,400	11,800
Fair Value on a Recurring Basis [Member] | Level 1 [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	47,121,000	86,574,000
Forward contracts	0	0
Insurance company contracts	0	0
Total	47,121,000	86,574,000
Fair Value on a Recurring Basis [Member] | Level 2 [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	0	0
Forward contracts	485,000	1,661,000
Insurance company contracts	0	0
Total	485,000	1,661,000
Fair Value on a Recurring Basis [Member] | Level 3 [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	0	0
Forward contracts	0	0
Insurance company contracts	27,292,000	26,280,000
Total	$ 27,292,000	$ 26,280,000