Summary of Significant Accounting Policies - Effect of ASC 606 (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents	$ 99,565	$ 51,562	$ 51,562	$ 53,148
Short-term investments	159,210	39,178	39,178
Accounts receivable, net of allowance for doubtful accounts of $1,624 and $1,478 at December 31, 2018 and 2017, respectively	74,935	73,661	73,661
Deferred contract acquisition and fulfillment costs, current portion	12,321	7,844	0
Prepaid expenses and other current assets	9,746	8,907	8,877
Long-term investments	44,892	1,102	1,102
Property and equipment, net	17,523	8,589	8,589
Goodwill	88,420	83,164	83,164	75,110
Intangible assets, net	23,955	16,640	16,640
Deferred contract acquisition and fulfillment costs, non-current portion	27,634	19,321	0
Other assets	1,168	1,363	1,363
Total assets	559,369	311,331	284,136
Accounts payable	7,048	2,240	2,240
Accrued expenses	37,376	29,728	29,728
Deferred revenue, current portion	189,855	142,020	155,811
Other current liabilities	707	1,706	1,706
Deferred revenue, non-current portion	58,716	83,373	68,689
Other long-term liabilities	3,660	2,238	1,809
Total liabilities	472,050	261,305	259,983
Common stock, $0.01 par value per share; 100,000,000 shares authorized at December 31, 2018 and 2017; 48,087,257 and 44,540,544 shares issued at December 31, 2018 and 2017, respectively; 47,600,449 and 44,053,736 shares outstanding at December 31, 2018 and 2017, respectively	476	441	441
Treasury stock	(4,764)	(4,764)	(4,764)
Additional paid-in-capital	556,223	463,428	463,428
Accumulated other comprehensive loss	(31)	(39)	(39)
Accumulated deficit	(464,585)	(409,040)	(434,913)
Total stockholders’ equity	87,319	50,026	24,153	$ 42,038	$ 68,075
Total liabilities and stockholders’ equity	559,369	311,331	284,136
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents	99,565		51,562
Short-term investments	159,210		39,178
Accounts receivable, net of allowance for doubtful accounts of $1,624 and $1,478 at December 31, 2018 and 2017, respectively	74,935		73,661
Deferred contract acquisition and fulfillment costs, current portion	0		0
Prepaid expenses and other current assets	9,281		8,877
Long-term investments	44,892		1,102
Property and equipment, net	17,523		8,589
Goodwill	88,420		83,164
Intangible assets, net	23,955		16,640
Deferred contract acquisition and fulfillment costs, non-current portion	0		0
Other assets	1,168		1,363
Total assets	518,949		284,136
Accounts payable	7,048		2,240
Accrued expenses	37,376		29,728
Deferred revenue, current portion	193,763		155,811
Other current liabilities	707		1,706
Deferred revenue, non-current portion	41,658		68,689
Other long-term liabilities	2,912		1,809
Total liabilities	458,152		259,983
Common stock, $0.01 par value per share; 100,000,000 shares authorized at December 31, 2018 and 2017; 48,087,257 and 44,540,544 shares issued at December 31, 2018 and 2017, respectively; 47,600,449 and 44,053,736 shares outstanding at December 31, 2018 and 2017, respectively	476		441
Treasury stock	(4,764)		(4,764)
Additional paid-in-capital	556,223		463,428
Accumulated other comprehensive loss	(31)		(39)
Accumulated deficit	(491,107)		(434,913)
Total stockholders’ equity	60,797		24,153
Total liabilities and stockholders’ equity	$ 518,949		$ 284,136
Term And Perpetual License [Member] | Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents		0
Short-term investments		0
Accounts receivable, net of allowance for doubtful accounts of $1,624 and $1,478 at December 31, 2018 and 2017, respectively		0
Deferred contract acquisition and fulfillment costs, current portion		0
Prepaid expenses and other current assets		0
Long-term investments		0
Property and equipment, net		0
Goodwill		0
Intangible assets, net		0
Deferred contract acquisition and fulfillment costs, non-current portion		0
Other assets		0
Total assets		0
Accounts payable		0
Accrued expenses		0
Deferred revenue, current portion		(10,912)
Other current liabilities		0
Deferred revenue, non-current portion		17,647
Other long-term liabilities		0
Total liabilities		6,735
Common stock, $0.01 par value per share; 100,000,000 shares authorized at December 31, 2018 and 2017; 48,087,257 and 44,540,544 shares issued at December 31, 2018 and 2017, respectively; 47,600,449 and 44,053,736 shares outstanding at December 31, 2018 and 2017, respectively		0
Treasury stock		0
Additional paid-in-capital		0
Accumulated other comprehensive loss		0
Accumulated deficit		(6,735)
Total stockholders’ equity		(6,735)
Total liabilities and stockholders’ equity		0
Professional Services [Member] | Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents		0
Short-term investments		0
Accounts receivable, net of allowance for doubtful accounts of $1,624 and $1,478 at December 31, 2018 and 2017, respectively		0
Deferred contract acquisition and fulfillment costs, current portion		0
Prepaid expenses and other current assets		30
Long-term investments		0
Property and equipment, net		0
Goodwill		0
Intangible assets, net		0
Deferred contract acquisition and fulfillment costs, non-current portion		0
Other assets		0
Total assets		30
Accounts payable		0
Accrued expenses		0
Deferred revenue, current portion		(1,523)
Other current liabilities		0
Deferred revenue, non-current portion		(2,624)
Other long-term liabilities		0
Total liabilities		(4,147)
Common stock, $0.01 par value per share; 100,000,000 shares authorized at December 31, 2018 and 2017; 48,087,257 and 44,540,544 shares issued at December 31, 2018 and 2017, respectively; 47,600,449 and 44,053,736 shares outstanding at December 31, 2018 and 2017, respectively		0
Treasury stock		0
Additional paid-in-capital		0
Accumulated other comprehensive loss		0
Accumulated deficit		4,177
Total stockholders’ equity		4,177
Total liabilities and stockholders’ equity		30
Timing Of Transfer Of Good Or Service, Other [Member] | Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents		0
Short-term investments		0
Accounts receivable, net of allowance for doubtful accounts of $1,624 and $1,478 at December 31, 2018 and 2017, respectively		0
Deferred contract acquisition and fulfillment costs, current portion		0
Prepaid expenses and other current assets		0
Long-term investments		0
Property and equipment, net		0
Goodwill		0
Intangible assets, net		0
Deferred contract acquisition and fulfillment costs, non-current portion		0
Other assets		0
Total assets		0
Accounts payable		0
Accrued expenses		0
Deferred revenue, current portion		(1,356)
Other current liabilities		0
Deferred revenue, non-current portion		(339)
Other long-term liabilities		0
Total liabilities		(1,695)
Common stock, $0.01 par value per share; 100,000,000 shares authorized at December 31, 2018 and 2017; 48,087,257 and 44,540,544 shares issued at December 31, 2018 and 2017, respectively; 47,600,449 and 44,053,736 shares outstanding at December 31, 2018 and 2017, respectively		0
Treasury stock		0
Additional paid-in-capital		0
Accumulated other comprehensive loss		0
Accumulated deficit		1,695
Total stockholders’ equity		1,695
Total liabilities and stockholders’ equity		0
Costs To Obtain Or Fulfill A Contract [Member] | Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents		0
Short-term investments		0
Accounts receivable, net of allowance for doubtful accounts of $1,624 and $1,478 at December 31, 2018 and 2017, respectively		0
Deferred contract acquisition and fulfillment costs, current portion		7,844
Prepaid expenses and other current assets		0
Long-term investments		0
Property and equipment, net		0
Goodwill		0
Intangible assets, net		0
Deferred contract acquisition and fulfillment costs, non-current portion		19,321
Other assets		0
Total assets		27,165
Accounts payable		0
Accrued expenses		0
Deferred revenue, current portion		0
Other current liabilities		0
Deferred revenue, non-current portion		0
Other long-term liabilities		429
Total liabilities		429
Common stock, $0.01 par value per share; 100,000,000 shares authorized at December 31, 2018 and 2017; 48,087,257 and 44,540,544 shares issued at December 31, 2018 and 2017, respectively; 47,600,449 and 44,053,736 shares outstanding at December 31, 2018 and 2017, respectively		0
Treasury stock		0
Additional paid-in-capital		0
Accumulated other comprehensive loss		0
Accumulated deficit		26,736
Total stockholders’ equity		26,736
Total liabilities and stockholders’ equity		$ 27,165