Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 02, 2021 Company shares	Feb. 28, 2021 TradingDay Company shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Capitalized compensation cost | $					$ 5,108	$ 5,284
Software and Capitalized Software Costs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Capitalized compensation cost | $			$ 1,700	$ 1,600	$ 5,100	5,300
Chief Sales Officer Holly Faurot [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Performance share units	5,445
Number of publicly traded companies | Company	34
Restricted Stock [Member] | Share Based Compensation Award V W A P Equals Or Exceeds Five Twenty Per Share | Non Executive Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Vesting percentage, restricted shares					50.00%
VWAP Share Price | $ / shares					$ 520
Restricted Stock [Member] | Time-Based Shares [Member] | Non Executive Employees [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights					3 years
Restricted Stock [Member] | Time-Based Shares [Member] | Non Executive Employees [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights					4 years
Restricted Stock [Member] | Share Based Compensation Award V W A P Equals Or Exceeds Six Hundred Per Share | Non Executive Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Vesting percentage, restricted shares					50.00%
VWAP Share Price | $ / shares					$ 600
Restricted Stock [Member] | LTIP [Member] | Non-executive Employees and Non-employee Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted shares of common stock issued					180,735
Restricted Stock [Member] | LTIP [Member] | Market-Based Shares [Member] | Non Executive Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted shares of common stock issued					42,934
Restricted Stock [Member] | LTIP [Member] | Time-Based Shares [Member] | Non-executive Employees and Non-employee Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted shares of common stock issued					137,801
Restricted Stock [Member] | LTIP [Member] | Time-Based Shares [Member] | Non-Employee Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted shares of common stock issued			230		3,558
Share-based compensation arrangement by share-based payment award, award vesting rights			In September 2021, Janet Haugen tendered her resignation from our Board of Directors. As a result of Ms. Haugen’s resignation, the compensation committee of the Board of Directors determined to accelerate the vesting of 297 shares of Ms. Haugen’s unvested shares of restricted stock, which was approximately one-half of the shares of restricted stock awarded to Ms. Haugen in 2021. Subsequent to Ms. Haugen’s resignation, the Board of Directors appointed Sharen Turney to serve as a Class I director to fill the resulting vacancy. Ms. Turney received a prorated portion of the standard compensation package for the Company’s non-management directors, which included 230 shares of restricted stock, and which will vest on May 10, 2022.		Such shares of restricted stock will cliff-vest on the seventh day following the first anniversary of the date of grant, provided that such director is providing services to the Company through the applicable vesting date, and subject to the terms and conditions of the LTIP and the applicable restricted stock award agreement.
Number of shares vested in period			297
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted shares of common stock issued					57,900
Performance Shares [Member] | LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of trading day | TradingDay		60
Number of publicly traded companies | Company		34
Performance Shares [Member] | LTIP [Member] | Executive Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Performance share units		52,470
Performance Shares [Member] | LTIP [Member] | Executive Officers [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Performance share units		131,176
Performance Shares [Member] | LTIP [Member] | Two-Year Performance Period [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Performance period commencement date		Jan. 01, 2021
Performance period maturity date		Dec. 31, 2022
Percentage of PSUs eligible to vest		25.00%
Deadline for vesting of shares		Mar. 01, 2023
Performance Shares [Member] | LTIP [Member] | Three-Year Performance Period [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Performance period commencement date		Jan. 01, 2021
Performance period maturity date		Dec. 31, 2023
Percentage of PSUs eligible to vest		75.00%
Deadline for vesting of shares		Feb. 29, 2024
Restricted Stock Awards and PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense | $			$ 29,000	$ 19,500	$ 76,400	$ 56,500