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Share Based Payments - Summary of Stock Options Outstanding and Exercisable (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	2,368,646	2,448,646
Exercise Price	$ 7.50	$ 7.35
Number of Options Exercisable	1,371,739
Employee and Director Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	2,016,646
Number of Options Exercisable	1,110,739
Employee and Director Stock Options | Option One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	360,000
Expiration Date	Jun. 18, 2019
Options Outstanding Remaining Contractual Life (In Years)	1 year 2 months 19 days
Exercise Price	$ 3.00
Grant Date Fair Value	$ 1.00
Number of Options Exercisable	360,000
Employee and Director Stock Options | Option Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	80,000
Expiration Date	Jun. 18, 2019
Options Outstanding Remaining Contractual Life (In Years)	1 year 2 months 19 days
Exercise Price	$ 3.00
Grant Date Fair Value	$ 1.32
Number of Options Exercisable	80,000
Employee and Director Stock Options | Option Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	20,000
Expiration Date	Dec. 08, 2019
Options Outstanding Remaining Contractual Life (In Years)	1 year 8 months 8 days
Exercise Price	$ 14.60
Grant Date Fair Value	$ 6.55
Number of Options Exercisable	20,000
Employee and Director Stock Options | Option Four
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	80,000
Expiration Date	Dec. 08, 2019
Options Outstanding Remaining Contractual Life (In Years)	1 year 8 months 8 days
Exercise Price	$ 14.80
Grant Date Fair Value	$ 6.46
Number of Options Exercisable	80,000
Employee and Director Stock Options | Option Five
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	20,000
Expiration Date	Mar. 16, 2020
Options Outstanding Remaining Contractual Life (In Years)	1 year 11 months 15 days
Exercise Price	$ 16.00
Grant Date Fair Value	$ 7.09
Number of Options Exercisable	20,000
Employee and Director Stock Options | Option Six
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	8,500
Expiration Date	Aug. 14, 2020
Options Outstanding Remaining Contractual Life (In Years)	2 years 4 months 17 days
Exercise Price	$ 4.90
Grant Date Fair Value	$ 1.94
Number of Options Exercisable	8,500
Employee and Director Stock Options | Option Seven
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	150,000
Expiration Date	Oct. 21, 2020
Options Outstanding Remaining Contractual Life (In Years)	2 years 6 months 21 days
Exercise Price	$ 4.20
Grant Date Fair Value	$ 1.80
Number of Options Exercisable	112,500
Employee and Director Stock Options | Option Eight
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	20,000
Expiration Date	Dec. 31, 2020
Options Outstanding Remaining Contractual Life (In Years)	2 years 9 months 3 days
Exercise Price	$ 6.20
Grant Date Fair Value	$ 2.49
Number of Options Exercisable	20,000
Employee and Director Stock Options | Option Nine
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	595,000
Expiration Date	Jul. 13, 2020
Options Outstanding Remaining Contractual Life (In Years)	2 years 3 months 14 days
Exercise Price	$ 6.95
Grant Date Fair Value	$ 3.23
Number of Options Exercisable	396,666
Employee and Director Stock Options | Option Ten
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	20,000
Expiration Date	Aug. 08, 2020
Options Outstanding Remaining Contractual Life (In Years)	2 years 4 months 9 days
Exercise Price	$ 6.55
Grant Date Fair Value	$ 3.23
Number of Options Exercisable	10,000
Employee and Director Stock Options | Option Eleven
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	617,000
Expiration Date	Apr. 17, 2027
Options Outstanding Remaining Contractual Life (In Years)	9 years 18 days
Exercise Price	$ 10.80
Grant Date Fair Value	$ 7.76
Employee and Director Stock Options | Option Twelve
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	6,146
Expiration Date	May 18, 2027
Options Outstanding Remaining Contractual Life (In Years)	9 years 1 month 20 days
Exercise Price	$ 10.00
Grant Date Fair Value	$ 5.23
Number of Options Exercisable	3,073
Employee and Director Stock Options | Option Thirteen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	10,000
Expiration Date	May 18, 2027
Options Outstanding Remaining Contractual Life (In Years)	9 years 1 month 20 days
Exercise Price	$ 10.00
Grant Date Fair Value	$ 7.63
Employee and Director Stock Options | Option Fourteen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	30,000
Expiration Date	Aug. 08, 2027
Options Outstanding Remaining Contractual Life (In Years)	9 years 4 months 9 days
Exercise Price	$ 13.15
Grant Date Fair Value	$ 8.86
Non-employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	352,000
Number of Options Exercisable	261,000
Non-employee Stock Options | Option One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	80,000
Expiration Date	Jun. 18, 2019
Options Outstanding Remaining Contractual Life (In Years)	1 year 2 months 19 days
Exercise Price	$ 3.00
Grant Date Fair Value	$ 1.32
Number of Options Exercisable	80,000
Non-employee Stock Options | Option Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	30,000
Expiration Date	Dec. 08, 2019
Options Outstanding Remaining Contractual Life (In Years)	1 year 8 months 8 days
Exercise Price	$ 14.60
Grant Date Fair Value	$ 8.25
Number of Options Exercisable	30,000
Non-employee Stock Options | Option Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	82,000
Expiration Date	Oct. 03, 2020
Options Outstanding Remaining Contractual Life (In Years)	2 years 9 months 3 days
Exercise Price	$ 6.75
Grant Date Fair Value	$ 4.00
Number of Options Exercisable	41,000
Non-employee Stock Options | Option Four
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	110,000
Expiration Date	Oct. 28, 2020
Options Outstanding Remaining Contractual Life (In Years)	2 years 6 months 3 days
Exercise Price	$ 4.20
Grant Date Fair Value	$ 2.20
Number of Options Exercisable	110,000
Non-employee Stock Options | Option Five
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	20,000
Expiration Date	May 18, 2027
Options Outstanding Remaining Contractual Life (In Years)	9 years 1 month 20 days
Exercise Price	$ 10.00
Grant Date Fair Value	$ 8.69
Non-employee Stock Options | Option Six
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	15,000
Expiration Date	Aug. 08, 2027
Options Outstanding Remaining Contractual Life (In Years)	9 years 4 months 9 days
Exercise Price	$ 13.15
Grant Date Fair Value	$ 11.70
Non-employee Stock Options | Option Seven
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding	15,000
Expiration Date	Nov. 06, 2027
Options Outstanding Remaining Contractual Life (In Years)	9 years 7 months 9 days
Exercise Price	$ 20.65
Grant Date Fair Value	$ 19.93

X

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Expiration date of the option.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Footnote 5

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

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