Equity Compensation Plans - 1996 Employee Stock Purchase Plan (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Value of stock purchases made pursuant to employee stock purchase plan	$ 1,547	$ 1,394	$ 1,347
1996 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issue to employees under the employee stock purchase plan	1,700,000
Purchase Price of shares as a percentage of market value	85.00%
Issuance of common stock pursuant to employee stock purchase plan, shares	58,927	61,592	68,845
Value of stock purchases made pursuant to employee stock purchase plan	$ 1,600	$ 1,400	$ 1,400
Remaining number of shares eligible for purchase under employee stock purchase plan	440,622
1996 Employee Stock Purchase Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of shares under the plan	$ 20.84	$ 21.31	$ 16.01
1996 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of shares under the plan	$ 30.58	$ 25.47	$ 24.99

Remaining number of shares eligible for purchase under employee stock purchase plan.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ 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 (a)(3)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The weighted average of per share prices paid for shares purchased on the open market for issuance to employees under the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30
-Article 5

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Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

+ References

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