Income Taxes - Summary of Tax Credit Carryforwards (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Tax Credit Carryforward [Line Items]
Tax Credit Carryforwards	$ 57,019us-gaap_TaxCreditCarryforwardAmount
United States [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforwards	35,261
Canada [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforwards	$ 21,758

The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Carryforwards

-URI http://asc.fasb.org/extlink&oid=6506874

Name:	us-gaap_TaxCreditCarryforwardAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant