The Company’s significant accounting policies are discussed in Note 2 to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022. There have been no significant changes to these policies during the three and nine months ended September 30, 2023. The following describes the impact of certain policies.

The Company applies ASC 606 and follows a five-step model to determine the appropriate amount of revenue to be recognized in accordance with ASC 606.

The Company separates revenue into subscription and non-subscription categories to disaggregate the revenue that is term-based and renewable from the revenue that is one-time in nature. Revenue from subscription and non-subscription contractual arrangements were as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
	(in thousands)
SaaS subscription and support and maintenance	$	133,626	$	112,351	$	380,954	$	312,992
On‑premise subscription	4,895		6,173		15,388		17,140
Subscription revenue	138,521		118,524		396,342		330,132
Professional services	3,956		5,216		12,594		14,187
Perpetual licenses	148		817		990		4,134
Non‑subscription revenue	4,104		6,033		13,584		18,321
Total revenue	$	142,625	$	124,557	$	409,926	$	348,453

Contract liabilities consist of customer billings in advance of revenue being recognized. The Company invoices its customers for subscription, support and maintenance, and services in advance. Changes in contract liabilities, including revenue earned during the period from the beginning contract liability balance and new deferrals of revenue during the period, were as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
	(in thousands)
Balance, beginning of the period	$	355,051	$	316,952	$	346,150	$	282,128
Acquisitions	3,230		—		3,230		—
Revenue earned	(114,780)		(96,542)		(250,724)		(199,357)
Deferral of revenue	127,803		120,820		272,274		258,459
Other (1)	(1,550)		—		(1,176)		—
Balance, end of the period	$	369,754	$	341,230	$	369,754	$	341,230

(1) Includes contract assets netted against contract liabilities on a contract-by-contract basis.

There were no significant changes to our contract liabilities during the three and nine months ended September 30, 2023 and 2022 outside of our sales activities.

Revenue allocated to remaining performance obligations represents contracted revenue that has not yet been recognized, which includes deferred revenue and noncancellable amounts to be invoiced. As of September 30, 2023, the Company had $477.4 million of remaining performance obligations, with 72% expected to be recognized as revenue over the succeeding 12 months, and the remainder generally expected to be recognized over the three years thereafter.

Sales commissions, as well as associated payroll taxes and retirement plan contributions (together, contract costs), that are incremental to the acquisition of customer contracts are capitalized using a portfolio approach as deferred contract costs in the condensed consolidated balance sheets when the period of benefit is determined to be greater than one year.

Total amortization of contract costs was $5.6 million and $4.2 million for the three months ended September 30, 2023 and 2022, respectively, and $15.6 million and $12.1 million for the nine months ended September 30, 2023 and 2022, respectively.

The Company periodically reviews these deferred contract costs to determine whether events or changes in circumstances have occurred that could affect the period of benefit of these deferred contract costs. There were no impairment losses recorded during the three and nine months ended September 30, 2023 and 2022.