Shareholders' Equity - Summary of Certain Additional Information about Stock Options (Detail) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted average grant-date fair value of options granted during the period	$ 1.77	$ 2.64	$ 1.98	$ 2.80
Options in-the-money (in shares)	19,550	1,755,762	19,550	1,755,762
Aggregate intrinsic value of options exercised during the period	$ 1,578	$ 17,412	$ 1,853	$ 57,833

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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