8. Stock Plans (Details 2)	12 Months Ended
Dec. 31, 2017 $ / shares shares
Restricted Stock Units R S U [Member]
Shares
Beginning Balance \| shares	9,388
Granted \| shares	1,420
Vested \| shares	(4,608)
Ending Balance \| shares	6,200
Weighted Average Award Date Fair Value Per Share
Beginning Balance \| $ / shares	$ 258.69
Granted \| $ / shares	616.41
Vested \| $ / shares	230.90
Ending Balance \| $ / shares	$ 361.28
Director’s Stock Units [Member]
Shares
Beginning Balance \| shares	0
Granted \| shares	11
Vested \| shares	(11)
Ending Balance \| shares	0
Weighted Average Award Date Fair Value Per Share
Beginning Balance \| $ / shares	$ 0.00
Granted \| $ / shares	535.07
Vested \| $ / shares	535.07
Ending Balance \| $ / shares	$ 0.00
2006 Equity Incentive Plan \| Restricted Stock [Member]
Shares
Beginning Balance \| shares	1,500
Granted \| shares	5,900
Vested \| shares	(1,500)
Ending Balance \| shares	5,900
Weighted Average Award Date Fair Value Per Share
Beginning Balance \| $ / shares	$ 228.08
Granted \| $ / shares	445.47
Vested \| $ / shares	228.08
Ending Balance \| $ / shares	$ 445.47

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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No definition available.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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