Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Goodwill not subject to amortization	$ 1,888,889	$ 1,886,494
Core Deposit Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	105,165	105,165
Accumulated Amortization	(84,786)	(82,028)
George Mason Trade Name Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,080	1,080
Crescent Trade Name [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	196	196
Community Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	0
Goodwill not subject to amortization	1,883,574	1,881,179
Community Banking [Member] | Core Deposit Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	105,165	105,165
Accumulated Amortization	(84,786)	(82,028)
Community Banking [Member] | George Mason Trade Name Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	0
Community Banking [Member] | Crescent Trade Name [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	0
Mortgage Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,276	1,276
Goodwill not subject to amortization	5,315	5,315
Mortgage Banking [Member] | Core Deposit Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	0
Accumulated Amortization	0	0
Mortgage Banking [Member] | George Mason Trade Name Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,080	1,080
Mortgage Banking [Member] | Crescent Trade Name [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	196	196
Total Gross Carrying Amount [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,276	$ 1,276