Shareholders' Equity - Summary of Certain Additional Information about Stock Options (Detail) - USD ($)	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted average grant-date fair value for options granted during the period	$ 2.09	$ 3.01
Options in-the-money	737,632	1,224,182
Aggregate intrinsic value of options exercised during the period	$ 275	$ 40,421

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration