Collaboration and License Agreements - Additional Information (Detail) - USD ($)		1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2018	Jun. 30, 2018	Dec. 31, 2017	Feb. 28, 2017	May 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration and license revenue						$ 8,975,000	$ 9,029,000	$ 33,543,000	$ 26,196,000
Collaboration and License Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration and license revenue						8,975,000	9,029,000	33,543,000	26,196,000
Balance without adoption of ASC606 [Member] | Accounting Standards Update 2014-09 [Member] | Collaboration and License Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration and license revenue						4,727,000		23,849,000
Avacopan Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non refundable upfront payments received					$ 85,000,000			20,000,000
Non refundable upfront payment received in cash					60,000,000
Non refundable upfront payment received in equity investment					$ 25,000,000
Share price of common stock in equity investment					$ 7.50
Non refundable upfront payment received in equity investment, shares					3,333,333
Revenue recognized upon achievement of regulatory milestone			$ 50,000,000
Transaction price						153,000,000		153,000,000
Upfront payments received					$ 78,000,000
Non refundable upfront payments allocated for issuance of common stock					$ 7,000,000
Issuance of common stock, per share value					$ 2.10
Collaboration and license revenue						7,600,000		28,800,000
Avacopan Agreement [Member] | Balance without adoption of ASC606 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration and license revenue							6,200,000		18,200,000
CCX140 Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price						113,500,000		113,500,000
Upfront payments received										$ 50,000,000
Collaboration and license revenue						$ 1,500,000		4,800,000
Non refundable upfront commitment										$ 50,000,000
CCX140 Agreement [Member] | Balance without adoption of ASC606 [Member] | Accounting Standards Update 2014-09 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payments received	$ 50,000,000
CCX140 Agreement [Member] | Balance without adoption of ASC606 [Member] | Accounting Standards Update 2014-09 [Member] | Collaboration and License Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration and license revenue							$ 2,800,000		$ 8,000,000
CCX140 Agreement [Member] | Vifor [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development funding								58,500,000
Avacopan Letter Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payment for expanded rights		$ 5,000,000
CCX140 Letter Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payment for expanded rights		$ 5,000,000
Avacopan Amendment [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront cash commitment				$ 20,000,000
CCX140 Amendment [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non refundable upfront commitment								11,500,000
Maximum [Member] | Avacopan Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable								460,000,000
Maximum [Member] | CCX140 Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable								$ 625,000,000