Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 996,623	$ 833,458
Loans	14,357,460	11,666,572
Premises and equipment	492,384	295,060
Other assets	76,583	68,084
Total assets	21,259,143	16,543,337	$ 15,000,000
LIABILITIES
Long-term debt	435,859
Total liabilities	18,270,219	14,296,903
Stockholders’ equity:
Preferred stock	767
Common stock	1,136	923
Surplus	2,117,282	1,597,944
Accumulated other comprehensive gain (loss):	848,848	674,941
Total stockholders’ equity	2,988,924	2,246,434	$ 2,084,564	$ 1,151,111
Total liabilities and stockholders’ equity	21,259,143	16,543,337
Parent Company
ASSETS
Cash and cash equivalents	104,068	219,063
Investment securities	743	2,848
Investments in wholly-owned subsidiaries	3,269,224	2,368,870
Loans	657	774
Intangible assets, net	133	133
Premises and equipment	27,351	5,804
Other assets	31,738	29,974
Total assets	3,433,914	2,627,466
LIABILITIES
Long-term debt	413,760	353,950
Other liabilities	31,230	27,082
Total liabilities	444,990	381,032
Stockholders’ equity:
Preferred stock	767
Common stock	1,136	923
Surplus	2,117,282	1,597,944
Accumulated other comprehensive gain (loss):	848,848	674,941
Unrealized appreciation (depreciation) on available-for-sale securities, net of income taxes of $7,392 and ($9,686) at December 31, 2019 and 2018 respectively	20,891	(27,374)
Total stockholders’ equity	2,988,924	2,246,434
Total liabilities and stockholders’ equity	$ 3,433,914	$ 2,627,466