SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) subsidiary shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounting Policies
Recurring revenue percentage of total revenue (percent)	73.00%
Cash and investments	$ 758,500,000
Revolving line of credit	$ 0	$ 0
Number of wholly-owned subsidiaries | subsidiary	11
Accounts receivable, net	$ 403,700,000	396,500,000
Accounts receivable, allowance for losses	$ 9,255,000	5,738,000
Sales commission, renewal period	1 year
Research and development expense	$ 88,363,000	81,342,000	$ 63,264,000
Goodwill impairment loss	0
Impairments of intangible assets	0	0	0
Impairments of long-lived assets	0	0	0
Capitalized post acquisition software development costs	$ 5,800,000	4,800,000
Remaining estimated economic life	5 years
Amortization of software development costs	$ 1,200,000	300,000
Purchase of held to maturity securities	154,800,000
Interest receivable	896,000
Cost-method investment impairment	0	0	0
Cash and cash equivalents	603,623,000	232,682,000	$ 134,279,000	$ 185,926,000
Data And Insight
Accounting Policies
Goodwill assessed for impairment	75,700,000
Case Management, Business Process Management, Data And Insight
Accounting Policies
Goodwill assessed for impairment	$ 152,000,000.0
Percentage of total goodwill	18.00%
BFTR, LLC
Accounting Policies
Cost method investment	$ 10,000,000.0
Investment percentage	18.00%
Convertible Preferred Stock | Record Holdings Pty Limited
Accounting Policies
Cost method investment	$ 15,000,000.0
Investment percentage	20.00%
Minimum
Accounting Policies
Typical contract term (in years)	3 years
Contract term (in years)	1 year
Progress billing retention percentage	5.00%
Payment term	30 days
Sales commissions amortization period (in years)	3 years
Vesting period (in years)	3 years
Maximum
Accounting Policies
Typical contract term (in years)	5 years
Contract term (in years)	10 years
Progress billing retention percentage	20.00%
Payment term	90 days
Sales commissions amortization period (in years)	7 years
Vesting period (in years)	6 years
Stock Option Plan
Accounting Policies
Contractual term (in years)	10 years
Stock Option Plan | Minimum
Accounting Policies
Vesting period (in years)	3 years
Stock Option Plan | Maximum
Accounting Policies
Vesting period (in years)	6 years
Restricted Stock Units (RSUs) | Minimum
Accounting Policies
Vesting period (in years)	3 years
Restricted Stock Units (RSUs) | Maximum
Accounting Policies
Vesting period (in years)	5 years
Performance Shares
Accounting Policies
Share conversion rate (shares) | shares	1
Unbilled Revenues
Accounting Policies
Accounts receivable, net	$ 140,800,000	134,000,000.0
Unbilled Revenues | Retention Receivable
Accounting Policies
Accounts receivable, net	$ 13,100,000	$ 13,100,000
SaaS arrangements services | Minimum
Accounting Policies
Typical contract term (in years)	3 years
Contract term (in years)	1 year
SaaS arrangements services | Maximum
Accounting Policies
Typical contract term (in years)	5 years
Contract term (in years)	10 years
Appraisal services | Minimum
Accounting Policies
Contract term (in years)	1 year
Appraisal services | Maximum
Accounting Policies
Contract term (in years)	3 years
Revolving Credit Facility | Credit Agreement
Accounting Policies
Revolving line of credit	$ 0
Line of credit facility, unused borrowing capacity	$ 400,000,000