Summary of Changes in Accounts Receivable and Contract Liabilities (Deferred Revenue) (Detail) - EUSA - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price	$ 12,500	$ 10,500	$ 8,500
Ending Balance March 31, 2019	6,000
Accounting Standards Update 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price	12,500
Beginning Balance January 1, 2019	5,460
Additions	1,000
Deductions	(454)
Ending Balance March 31, 2019	6,006	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, 2019	$ 1,302
Deductions	(99)
Ending Balance March 31, 2019	1,203	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, 2019	$ 2,079
Deductions	(158)
Ending Balance March 31, 2019	1,921	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
Beginning Balance January 1, 2019	$ 1,040
Deductions	(79)
Ending Balance March 31, 2019	961	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
Beginning Balance January 1, 2019	$ 1,039
Deductions	(79)
Ending Balance March 31, 2019	960	1,039
Accounting Standards Update 2014-09 | Milestone - Spanish Reimbursement Approval
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Liabilities, Transaction Price	$ 2,000
Contract Liabilities, Date Achieved	2019-02
Additions	$ 1,000
Deductions	(39)
Ending Balance March 31, 2019	961
Accounting Standards Update 2014-09 | Accounts Receivable
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Beginning Balance January 1, 2019	187
Additions	2,157
Deductions	(187)
Ending Balance March 31, 2019	$ 2,157	$ 187