New Revenue Recognition Standard - Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Current assets:
Accounts receivable, net of allowance for doubtful accounts	$ 27,658		$ 32,260
Total current assets	309,520		277,746
Total assets	464,522		487,439
Current liabilities:
Deferred revenue	0		3,872
Total current liabilities	94,470		109,749
Deferred revenue, less current portion	0		315
Total liabilities	120,403		136,100
Stockholders’ equity:
Accumulated deficit	(481,948)		(502,107)
Total stockholders’ equity	344,119		351,339
Total liabilities and stockholders’ equity	464,522		$ 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	38
Total current assets	38
Total assets	38
Current liabilities:
Deferred revenue	2,308
Total current liabilities	2,308
Deferred revenue, less current portion	282
Total liabilities	2,590
Stockholders’ equity:
Accumulated deficit	(2,552)	$ 4,700
Total stockholders’ equity	(2,552)
Total liabilities and stockholders’ equity	38
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Current assets:
Accounts receivable, net of allowance for doubtful accounts	27,696
Total current assets	309,558
Total assets	464,560
Current liabilities:
Deferred revenue	2,308
Total current liabilities	96,778
Deferred revenue, less current portion	282
Total liabilities	122,993
Stockholders’ equity:
Accumulated deficit	(484,500)
Total stockholders’ equity	341,567
Total liabilities and stockholders’ equity	$ 464,560