Stock Option Plans - Summary of Options Outstanding (Details)	12 Months Ended
Dec. 31, 2017 $ / shares shares
Number outstanding \| shares	1,289,080
Number exercisable \| shares	814,180
$7.30-$10.38
Range of exercise prices, lower range	$ 7.30
Range of exercise prices, upper range	$ 10.38
Number outstanding \| shares	234,180
Options outstanding weighted-average remaining contractual life (years)	3 years
Options outstanding weighted-average exercise price	$ 9.57
Number exercisable \| shares	234,180
Options exercisable weighted-average exercise price	$ 9.57
$10.39-$13.68
Range of exercise prices, lower range	10.39
Range of exercise prices, upper range	$ 13.68
Number outstanding \| shares	218,250
Options outstanding weighted-average remaining contractual life (years)	4 years
Options outstanding weighted-average exercise price	$ 11.40
Number exercisable \| shares	218,250
Options exercisable weighted-average exercise price	$ 11.40
$13.69-$16.98
Range of exercise prices, lower range	13.69
Range of exercise prices, upper range	$ 16.98
Number outstanding \| shares	308,250
Options outstanding weighted-average remaining contractual life (years)	6 years
Options outstanding weighted-average exercise price	$ 15.44
Number exercisable \| shares	268,000
Options exercisable weighted-average exercise price	$ 15.26
$16.99-$24.43
Range of exercise prices, lower range	16.99
Range of exercise prices, upper range	$ 24.43
Number outstanding \| shares	313,500
Options outstanding weighted-average remaining contractual life (years)	9 years
Options outstanding weighted-average exercise price	$ 21.91
Number exercisable \| shares	72,750
Options exercisable weighted-average exercise price	$ 20.36
$24.44-$28.2
Range of exercise prices, lower range	24.44
Range of exercise prices, upper range	$ 28.20
Number outstanding \| shares	214,900
Options outstanding weighted-average remaining contractual life (years)	9 years
Options outstanding weighted-average exercise price	$ 25.31
Number exercisable \| shares	21,000
Options exercisable weighted-average exercise price	$ 28.16

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

+ 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)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

+ 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)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

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- Definition

Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

+ 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)(1)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

+ 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)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ 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 (e)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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