Allowance for Credit Losses (Schedule of Aging of the Company's Loan Portfolio) (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 151,116	$ 105,908	$ 105,847
90+ days and still accruing	37,168	34,376	16,105
Current	30,968,939	26,361,332	24,998,685
Total Loans	31,402,903	26,800,290	25,304,659
60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	79,295	50,523	54,908
30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	166,385	248,151	129,114
Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual	42,882	37,224	47,604
90+ days and still accruing	1,374	1,855	1,939
Current	8,446,936	8,166,242	8,199,846
Total Loans	8,523,864	8,285,920	8,270,774
Commercial | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	8,952	3,275	5,283
Commercial | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	23,720	77,324	16,102
Commercial PPP Loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	0	0	0
Current	3,335,368	0	0
Total Loans	3,335,368	0	0
Commercial PPP Loans | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	0
Commercial PPP Loans | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	0
Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	9,829	2,112	2,256
90+ days and still accruing	0	3,514	0
Current	1,310,962	1,223,567	971,631
Total Loans	1,340,048	1,283,449	1,000,393
Construction and development | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	1,944	5,292	577
Construction and development | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	17,313	48,964	25,929
Non-construction
Financing Receivable, Past Due [Line Items]
Nonaccrual	54,728	24,001	18,619
90+ days and still accruing	0	11,432	5,124
Current	6,723,218	6,626,537	6,194,428
Total Loans	6,860,697	6,736,827	6,275,851
Non-construction | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	24,536	26,254	10,622
Non-construction | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	58,215	48,603	47,058
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	7,261	7,363	8,489
90+ days and still accruing	0	0	0
Current	458,039	501,716	516,405
Total Loans	466,596	513,066	527,370
Home equity | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	454	321
Home equity | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	1,296	3,533	2,155
Residential real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual	19,529	13,797	14,236
90+ days and still accruing	0	5,771	1,867
Current	1,401,994	1,313,523	1,098,937
Total Loans	1,427,429	1,354,221	1,118,178
Residential real estate | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	1,506	3,089	1,306
Residential real estate | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	4,400	18,041	1,832
Premium finance receivables - commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual	16,445	20,590	13,833
90+ days and still accruing	35,638	11,517	6,940
Current	3,865,168	3,379,018	3,313,535
Total Loans	3,999,774	3,442,027	3,368,423
Premium finance receivables - commercial | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	35,967	12,119	17,977
Premium finance receivables - commercial | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	46,556	18,783	16,138
Premium finance receivables - life
Financing Receivable, Past Due [Line Items]
Nonaccrual	15	590	590
90+ days and still accruing	0	0	0
Current	5,379,797	5,041,453	4,595,635
Total Loans	5,400,802	5,074,602	4,634,478
Premium finance receivables - life | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	6,386	0	18,580
Premium finance receivables - life | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	14,604	32,559	19,673
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	427	231	220
90+ days and still accruing	156	287	235
Current	47,457	109,276	108,268
Total Loans	48,325	110,178	109,192
Consumer and other | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	4	40	242
Consumer and other | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	$ 281	$ 344	$ 227