Summary of Changes in Accounts Receivable and Contract Liabilities (Deferred Revenue) (Detail) - EUSA - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price	$ 10,500	$ 8,500
Ending Balance December 31, 2018	5,500		$ 5,500
Accounting Standards Update 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price			10,500
Beginning Balance January 1, 2018		4,408	4,408
Additions			2,395
Deductions			(1,343)
Ending Balance December 31, 2018	5,460		5,460
Accounting Standards Update 2014-09 | Upfront Payment
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price			$ 2,500
Contract Liabilities, Date Achieved			2015-12
Contract Liabilities Date Paid			2015-12
Beginning Balance January 1, 2018		1,697	$ 1,697
Deductions			(395)
Ending Balance December 31, 2018	1,302		1,302
Accounting Standards Update 2014-09 | R&D Payment - EMA Approval in RCC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price			$ 4,000
Contract Liabilities, Date Achieved			2017-08
Contract Liabilities Date Paid			2017-09
Beginning Balance January 1, 2018		2,711	$ 2,711
Deductions			(632)
Ending Balance December 31, 2018	2,079		2,079
Accounting Standards Update 2014-09 | Milestone - UK Reimbursement Approval
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price			$ 2,000
Contract Liabilities, Date Achieved			2018-02
Contract Liabilities Date Paid			2018-03
Additions			$ 1,316
Deductions			(276)
Ending Balance December 31, 2018	1,040		1,040
Accounting Standards Update 2014-09 | Milestone - German Reimbursement Approval
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price			$ 2,000
Contract Liabilities, Date Achieved			2018-11
Contract Liabilities Date Paid			2018-12
Additions			$ 1,079
Deductions			(40)
Ending Balance December 31, 2018	1,039		1,039
Accounting Standards Update 2014-09 | Accounts Receivable
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Beginning Balance January 1, 2018		$ 18	18
Additions			4,462
Deductions			(4,293)
Ending Balance December 31, 2018	$ 187		$ 187