Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
U.S. federal corporate tax rate	21.00%	34.00%
Avacopan and CCX140 Agreement [Member]
Significant Accounting Policies [Line Items]
Royalty revenue resulting from collaboration arrangements	$ 0	$ 0
Accounting Standards Update 2014-09 [Member] \| Accumulated Deficit [Member]
Significant Accounting Policies [Line Items]
Cumulative effect of adoption to opening balance of accumulated deficit	$ 47,300,000

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration