New Revenue Recognition Standard - Condensed Consolidated Statement of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Total revenues	$ 24,168	$ 34,301	$ 54,662	$ 63,402
Loss from operations	(34,311)	(18,609)	(59,576)	(40,518)
Loss before income taxes	13,747	(20,597)	(2,068)	(44,344)
Net loss	$ 13,744	$ (20,852)	$ (2,074)	$ (44,398)
Net income per share:
Basic ($ per share)	$ 0.13	$ (0.27)	$ (0.02)	$ (0.57)
Diluted ($ per share)	$ 0.13	$ (0.27)	$ (0.02)	$ (0.57)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue:
Total revenues	$ 1,109		$ 1,626
Loss from operations	1,109		1,626
Loss before income taxes	1,109		1,626
Net loss	$ 1,109		$ 1,626
Net income per share:
Basic ($ per share)	$ 0.01		$ 0.02
Diluted ($ per share)	$ 0.01		$ 0.02
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue:
Total revenues	$ 25,277		$ 56,288
Loss from operations	(33,202)		(57,950)
Loss before income taxes	14,856		(442)
Net loss	$ 14,853		$ (448)
Net income per share:
Basic ($ per share)	$ 0.14		$ 0.00
Diluted ($ per share)	$ 0.14		$ 0.00
Product [Member]
Revenue:
Total revenues	$ 23,753	$ 31,156	$ 51,863	$ 57,001
Product [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue:
Total revenues	1,165		1,562
Product [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue:
Total revenues	24,918		53,425
License and Service [Member]
Revenue:
Total revenues	415	$ 3,145	2,799	$ 6,401
License and Service [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue:
Total revenues	(56)		64
License and Service [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue:
Total revenues	$ 359		$ 2,863