Parent Company Financial Information - STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 59,553	$ 158,068	$ 123,340
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense	10,859	10,528	9,033
Deferred income tax (benefit) expense	(42,622)	7,496	9,275
Change in accrued expenses and other liabilities, net	(9,455)	(6,265)	14,157
Net cash provided by (used in) operating activities	212,298	182,690	196,491
Cash flows from investing activities:
Change in cash acquired in acquisitions, net	937,100	0	146,571
Net cash provided by (used in) investing activities	570,483	(98,251)	(137,493)
Cash flows from financing activities:
Redemption of junior subordinated debt securities	0	(18,558)	0
Proceeds from issuance of subordinated debt, net	147,359	122,453	0
Cash dividends paid	(79,901)	(53,867)	0
Repurchase and retirement of common stock	0	(100,000)	0
Restricted stock surrendered and canceled	(1,653)	(3,285)	(1,669)
Net cash (used in) provided by financing activities	(228,865)	39,005	(52,756)
Net change in cash and cash equivalents	553,916	123,444	6,242
Cash and cash equivalents, beginning of year	326,850	203,406	197,164
Cash and cash equivalents, end of year	880,766	326,850	203,406
Corporation
Cash flows from operating activities:
Net income	60,351	159,718	123,340
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense	10,859	10,528	9,033
Equity in undistributed earnings of subsidiary and dividends from the bank	(48,451)	(117,458)	(132,460)
Deferred income tax (benefit) expense	188	42	65
Change in accrued expenses and other liabilities, net	1,149	3,131	(4,149)
Change in accrued interest receivable and other assets, net	(8,443)	(4,826)	2,461
Net cash provided by (used in) operating activities	15,653	51,135	(1,710)
Cash flows from investing activities:
Change in cash acquired in acquisitions, net	0	0	2,985
Other, net	0	0	(5,467)
Net cash provided by (used in) investing activities	0	0	(2,482)
Cash flows from financing activities:
Redemption of junior subordinated debt securities	0	(18,558)	0
Proceeds from issuance of subordinated debt, net	147,359	122,453	0
Cash dividends paid	(79,901)	(53,867)	0
Repurchase and retirement of common stock	0	(100,000)	0
Proceeds from exercise of options	1,652	2,679	1,924
Restricted stock surrendered and canceled	(1,653)	(3,285)	(1,669)
Net cash (used in) provided by financing activities	67,457	(50,578)	255
Net change in cash and cash equivalents	83,110	557	(3,937)
Cash and cash equivalents, beginning of year	13,717	13,160	17,097
Cash and cash equivalents, end of year	$ 96,827	$ 13,717	$ 13,160