Significant Attributes of Deferred Tax Assets (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Carryforwards and tax credits		$ 91,832	$ 67,645
Tax credit carryforwards		$ 164,841	118,113
Operating Loss Carryforward expiration description	[1]	Varies
Domestic Tax Authority
Carryforwards and tax credits	[2]	$ 27,405	30,009
Domestic Tax Authority | Research Tax Credit Carryforward
Tax credit carryforwards		103,581	84,711
Domestic Tax Authority | Other Tax Credit Carryforward
Tax credit carryforwards		$ 5,742	3,075
Tax credit carryforwards date		Dec. 31, 2027
State and Local Jurisdiction | Georgia
Carryforwards and tax credits		$ 15,948	4,737
State and Local Jurisdiction | Pennsylvania
Carryforwards and tax credits		17,687	13,899
State and Local Jurisdiction | Other US States
Carryforwards and tax credits		12,236	4,495
State and Local Jurisdiction | Other US States | Research Tax Credit Carryforward
Tax credit carryforwards		21,310	16,545
State and Local Jurisdiction | California | Research Tax Credit Carryforward
Tax credit carryforwards		$ 34,208	13,782
Tax credit carryforwards expiration description		Indefinite
Foreign Tax Authority
Carryforwards and tax credits		$ 18,556	$ 14,505
Minimum | Domestic Tax Authority
Operating loss carryforwards date	[2]	Dec. 31, 2018
Minimum | Domestic Tax Authority | Research Tax Credit Carryforward
Tax credit carryforwards date		Dec. 31, 2018
Minimum | State and Local Jurisdiction | Georgia
Operating loss carryforwards date		Dec. 31, 2018
Minimum | State and Local Jurisdiction | Pennsylvania
Operating loss carryforwards date		Dec. 31, 2018
Minimum | State and Local Jurisdiction | Other US States
Operating loss carryforwards date		Dec. 31, 2018
Minimum | State and Local Jurisdiction | Other US States | Research Tax Credit Carryforward
Tax credit carryforwards date		Dec. 31, 2018
Maximum | Domestic Tax Authority
Operating loss carryforwards date	[2]	Dec. 31, 2037
Maximum | Domestic Tax Authority | Research Tax Credit Carryforward
Tax credit carryforwards date		Dec. 31, 2037
Maximum | State and Local Jurisdiction | Georgia
Operating loss carryforwards date		Dec. 31, 2037
Maximum | State and Local Jurisdiction | Pennsylvania
Operating loss carryforwards date		Dec. 31, 2037
Maximum | State and Local Jurisdiction | Other US States
Operating loss carryforwards date		Dec. 31, 2037
Maximum | State and Local Jurisdiction | Other US States | Research Tax Credit Carryforward
Tax credit carryforwards date		Dec. 31, 2037

[1] Canadian NOLs expire within 16 years and all other material foreign NOLs have an indefinite carryforward life.

[2] Gross of tax effect U.S. Federal operating loss carryforwards are $130.5 million for the year ended December 31, 2017 and $85.7 million for the year ended December 31, 2016.