Fair Value Measurements - Schedule of Fair Value Hierarchy of Financial Assets and Liabilities Carried at Fair Value and Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jul. 01, 2020	Dec. 31, 2019
Liabilities, Fair Value Disclosure [Abstract]
HKFS Contingent Consideration	$ 35,900
Honkamp Krueger Financial Services, Inc.
Liabilities, Fair Value Disclosure [Abstract]
HKFS Contingent Consideration	27,600	$ 27,600
Fair Value Measurements, Recurring
Cash equivalents:
Total assets at fair value	4,290		$ 4,264
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities at fair value	35,900
Fair Value Measurements, Recurring | Money Market and Other Funds
Cash equivalents:
Total cash equivalents	4,290		4,264
Fair Value Measurements, Recurring | Honkamp Krueger Financial Services, Inc.
Liabilities, Fair Value Disclosure [Abstract]
HKFS Contingent Consideration	35,900
Fair Value Measurements, Recurring | Quoted prices in active markets using identical assets (Level 1)
Cash equivalents:
Total assets at fair value	4,290		4,264
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities at fair value	0
Fair Value Measurements, Recurring | Quoted prices in active markets using identical assets (Level 1) | Money Market and Other Funds
Cash equivalents:
Total cash equivalents	4,290		4,264
Fair Value Measurements, Recurring | Quoted prices in active markets using identical assets (Level 1) | Honkamp Krueger Financial Services, Inc.
Liabilities, Fair Value Disclosure [Abstract]
HKFS Contingent Consideration	0
Fair Value Measurements, Recurring | Significant other observable inputs (Level 2)
Cash equivalents:
Total assets at fair value	0		0
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities at fair value	0
Fair Value Measurements, Recurring | Significant other observable inputs (Level 2) | Money Market and Other Funds
Cash equivalents:
Total cash equivalents	0		0
Fair Value Measurements, Recurring | Significant other observable inputs (Level 2) | Honkamp Krueger Financial Services, Inc.
Liabilities, Fair Value Disclosure [Abstract]
HKFS Contingent Consideration	0
Fair Value Measurements, Recurring | Significant unobservable inputs (Level 3)
Cash equivalents:
Total assets at fair value	0		0
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities at fair value	35,900
Fair Value Measurements, Recurring | Significant unobservable inputs (Level 3) | Money Market and Other Funds
Cash equivalents:
Total cash equivalents	0		$ 0
Fair Value Measurements, Recurring | Significant unobservable inputs (Level 3) | Honkamp Krueger Financial Services, Inc.
Liabilities, Fair Value Disclosure [Abstract]
HKFS Contingent Consideration	$ 35,900