New Revenue Recognition Standard - Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Current assets:
Accounts receivable, net of allowance for doubtful accounts	$ 29,485		$ 32,260
Total current assets	267,450		277,746
Total assets	412,627		487,439
Current liabilities:
Deferred revenue	0		3,872
Total current liabilities	100,945		109,749
Deferred revenue, less current portion	0		315
Total liabilities	125,849		136,100
Stockholders’ equity:
Accumulated deficit	(550,667)		(502,107)
Total stockholders’ equity	286,778		351,339
Total liabilities and stockholders’ equity	412,627		$ 487,439
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Current assets:
Accounts receivable, net of allowance for doubtful accounts	(216)
Total current assets	(216)
Total assets	(216)
Current liabilities:
Deferred revenue	1,885
Total current liabilities	1,885
Deferred revenue, less current portion	267
Total liabilities	2,152
Stockholders’ equity:
Accumulated deficit	(2,368)	$ 4,700
Total stockholders’ equity	(2,368)
Total liabilities and stockholders’ equity	(216)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Current assets:
Accounts receivable, net of allowance for doubtful accounts	29,269
Total current assets	267,234
Total assets	412,411
Current liabilities:
Deferred revenue	1,885
Total current liabilities	102,830
Deferred revenue, less current portion	267
Total liabilities	128,001
Stockholders’ equity:
Accumulated deficit	(553,035)
Total stockholders’ equity	284,410
Total liabilities and stockholders’ equity	$ 412,411