Business Combinations - Additional Information (Details) $ / shares in Units, € in Millions, $ in Millions								1 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	May 07, 2021 USD ($) $ / shares shares	Jan. 15, 2021 USD ($) $ / shares shares	Aug. 04, 2020 USD ($) $ / shares shares	May 27, 2020 USD ($) $ / shares shares	Mar. 19, 2020 USD ($) $ / shares shares	Feb. 25, 2020 USD ($) $ / shares shares	Feb. 07, 2020 USD ($) $ / shares shares	Aug. 31, 2021 NZD ($) shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2021 EUR (€) shares	Jun. 30, 2021 shares	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Business Acquisition [Line Items]
Cash paid													$ 199,679,000	$ 54,757,000
Contingent consideration															$ 10,619,000
Change in fair value of contingent consideration obligation													$ (7,046,000)	$ 1,500,000
Common stock reserved for future issuance | shares									5,700,000	5,700,000			5,700,000
xMatters Holdings, Inc
Business Acquisition [Line Items]
Date of acquisition of business	May 07, 2021
Total purchase price	$ 242,600,000
Cash paid	$ 178,100,000
Number of newly issued common stock | shares	555,332
Common stock price per share | $ / shares	$ 116.12
Weighted average useful life of identified acquired intangible assets													8 years 1 month 17 days
Cash paid													$ 165,498,000
xMatters Holdings, Inc | General and Administrative Expenses
Business Acquisition [Line Items]
Business acquisition transaction costs													1,500,000
Business acquisition expense													$ 700,000
xMatters Holdings, Inc | Acquired Technology
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													3 years
xMatters Holdings, Inc | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													9 years
xMatters Holdings, Inc | Trade Names
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													5 years
Red Sky Technologies Inc.
Business Acquisition [Line Items]
Date of acquisition of business		Jan. 15, 2021
Total purchase price		$ 55,400,000
Number of newly issued common stock | shares		162,820
Common stock price per share | $ / shares		$ 141.46
Weighted average useful life of identified acquired intangible assets													7 years 8 months 23 days
Cash paid		$ 32,400,000											$ 32,401,000
Contingent payment		30,000,000
Contingent consideration		$ 9,135,000
Change in fair value of contingent consideration obligation									$ (8,200,000)
Cash paid net of cash acquired									$ 400,000
Issuance of common stock for contingent consideration | shares									4,058	4,058
Red Sky Technologies Inc. | General and Administrative Expenses
Business Acquisition [Line Items]
Change in fair value of contingent consideration obligation									$ (8,200,000)
Red Sky Technologies Inc. | Maximum | General and Administrative Expenses
Business Acquisition [Line Items]
Business acquisition transaction costs													$ 100,000
Red Sky Technologies Inc. | Acquired Technology
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													3 years
Red Sky Technologies Inc. | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													9 years
Red Sky Technologies Inc. | Trade Names
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													4 years
Connexient
Business Acquisition [Line Items]
Date of acquisition of business							Feb. 07, 2020
Total purchase price							$ 20,200,000
Cash paid							$ 11,500,000
Number of newly issued common stock | shares							96,611
Common stock price per share | $ / shares							$ 93.32
Contingent payment							$ 6,000,000.0
CNL Software Limited
Business Acquisition [Line Items]
Date of acquisition of business						Feb. 25, 2020
Total purchase price						$ 35,700,000
Cash paid						$ 19,800,000
Number of newly issued common stock | shares						153,217
Common stock price per share | $ / shares						$ 104.10
One2Many Group B.V.
Business Acquisition [Line Items]
Date of acquisition of business					Mar. 19, 2020
Total purchase price					$ 13,100,000
Cash paid					$ 5,500,000
Number of newly issued common stock | shares					52,113
Common stock price per share | $ / shares					$ 104.95
Contingent payment					$ 15,000,000.0
Contingent consideration					2,200,000
Change in fair value of contingent consideration obligation									$ 1,100,000				$ 400,000
Cash paid net of cash acquired | €										€ 4.1
Issuance of common stock for contingent consideration | shares									41,668	41,668
Purchase liabilities					$ 2,000,000.0
One2Many Group B.V. | General and Administrative Expenses
Business Acquisition [Line Items]
Change in fair value of contingent consideration obligation									$ 1,100,000				$ 400,000
Techwan SA
Business Acquisition [Line Items]
Date of acquisition of business				May 27, 2020
Total purchase price				$ 15,500,000
Cash paid				$ 9,400,000
Number of newly issued common stock | shares				38,425
Common stock price per share | $ / shares				$ 132.05
Weighted average useful life of identified acquired intangible assets													7 years 5 months 19 days
Cash paid													$ 9,301,000
Contingent payment				$ 7,000,000.0
Contingent consideration				2,030,000
Purchase liabilities				$ 100,000
Common stock reserved for future issuance | shares				6,779
Techwan SA | General and Administrative Expenses
Business Acquisition [Line Items]
Business acquisition transaction costs															200,000
Techwan SA | Acquired Technology
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													3 years
Techwan SA | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													9 years
Techwan SA | Trade Names
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													3 years
SnapComms Limited
Business Acquisition [Line Items]
Date of acquisition of business			Aug. 04, 2020
Total purchase price			$ 34,400,000
Cash paid			$ 13,600,000					$ 2.5
Number of newly issued common stock | shares			121,858					12,390
Common stock price per share | $ / shares			$ 145.13
Weighted average useful life of identified acquired intangible assets													7 years 9 months 25 days
Cash paid													$ 10,090,000
Contingent payment			$ 5,000,000.0
Contingent consideration			$ 2,047,000
Change in fair value of contingent consideration obligation												$ 700,000
Issuance of common stock for contingent consideration | shares											6,188
SnapComms Limited | General and Administrative Expenses
Business Acquisition [Line Items]
Business acquisition transaction costs															$ 100,000
Change in fair value of contingent consideration obligation												$ 700,000
SnapComms Limited | Acquired Technology
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													3 years
SnapComms Limited | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													9 years
SnapComms Limited | Trade Names
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets													3 years