Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Cash and cash equivalents		$ 833,458	$ 598,042
Loans		11,666,572	10,738,017
Premises and equipment		295,060	287,249
Other assets		68,084	71,439
Total assets		16,543,337	15,055,806
LIABILITIES
Long-term debt		369,400
Total liabilities		14,296,903	12,971,242
Stockholders’ equity:
Common stock	[1]	923	920
Surplus		1,597,944	1,586,034
Accumulated other comprehensive loss		674,941	514,874
Total stockholders’ equity		2,246,434	2,084,564	$ 1,151,111	$ 1,076,855
Total liabilities and stockholders’ equity		16,543,337	15,055,806
Parent Company
ASSETS
Cash and cash equivalents		219,063	19,101
Investment securities		2,848	2,789
Investments in wholly-owned subsidiaries		2,368,870	2,288,687
Loans		774	993
Intangible assets, net		133	133
Premises and equipment		5,804	10,369
Other assets		29,974	31,181
Total assets		2,627,466	2,353,253
LIABILITIES
Short-term debt		0	75,000
Long-term debt		353,950	183,947
Other liabilities		27,082	9,742
Total liabilities		381,032	268,689
Stockholders’ equity:
Common stock		923	920
Surplus		1,597,944	1,586,034
Accumulated other comprehensive loss		674,941	514,874
Unrealized depreciation on available-for-sale securities, net of income taxes of ($9,686) and ($6,108) at December 31, 2018 and 2017 respectively		(27,374)	(17,264)
Total stockholders’ equity		2,246,434	2,084,564
Total liabilities and stockholders’ equity		$ 2,627,466	$ 2,353,253

[1] On April 19, 2018, shareholders of the Company approved an increase in the number of authorized shares from 120,000,000 to 175,000,000.