Parent Company Financial Information - STATEMENTS OF CASH FLOWS (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 41,098,000	$ 41,375,000	$ 38,527,000	$ 38,718,000	$ 39,643,000	$ 28,392,000	$ 27,303,000	$ 28,002,000	$ 158,068,000	$ 123,340,000	$ 60,100,000
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense									10,528,000	9,033,000	5,809,000
Change in accrued expenses and other liabilities, net									(6,265,000)	14,157,000	5,193,000
Net cash provided by (used) in operating activities									182,690,000	196,491,000	69,371,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash acquired in acquisitions, net									0	146,571,000	225,945,000
Net cash used in investing activities									(98,251,000)	(137,493,000)	(284,169,000)
Cash flows from financing activities:
Redemption of junior subordinated debt securities									(18,558,000)	0	0
Proceeds from issuance of subordinated debt, net									122,453,000	0	0
Cash dividends paid									(53,867,000)	0	0
Repurchase and retirement of common stock									(100,000,000)	0	0
Restricted stock surrendered and canceled									(3,285,000)	(1,669,000)	(1,258,000)
Net cash provided by (used in) financing activities									39,005,000	(52,756,000)	255,105,000
Net change in cash and cash equivalents									123,444,000	6,242,000	40,307,000
Cash and cash equivalents, beginning of year				203,406,000				197,164,000	203,406,000	197,164,000	156,857,000
Cash and cash equivalents, end of year	326,850,000				203,406,000				326,850,000	203,406,000	197,164,000
Corporation
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income									159,718,000	123,340,000	60,100,000
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense									10,528,000	9,033,000	5,809,000
Equity in undistributed earnings of subsidiary and dividends from the bank									(117,458,000)	(132,460,000)	(68,323,000)
Increase in current and deferred taxes									42,000	65,000	0
Change in accrued expenses and other liabilities, net									3,131,000	(4,149,000)	(365,000)
Change in accrued interest receivable and other assets, net									(4,826,000)	2,461,000	817,000
Net cash provided by (used) in operating activities									51,135,000	(1,710,000)	(1,962,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash acquired in acquisitions, net									0	2,985,000	0
Other, net									0	(5,467,000)	601,000
Net cash used in investing activities									0	(2,482,000)	601,000
Cash flows from financing activities:
Redemption of junior subordinated debt securities									(18,558,000)	0	0
Proceeds from issuance of subordinated debt, net									122,453,000	0	0
Cash dividends paid									(53,867,000)	0	0
Repurchase and retirement of common stock									(100,000,000)	0	0
Proceeds from exercise of options									2,679,000	1,924,000	4,592,000
Restricted stock surrendered and canceled									(3,285,000)	(1,669,000)	(1,258,000)
Net cash provided by (used in) financing activities									(50,578,000)	255,000	3,334,000
Net change in cash and cash equivalents									557,000	(3,937,000)	1,973,000
Cash and cash equivalents, beginning of year				$ 13,160,000				$ 17,097,000	13,160,000	17,097,000	15,124,000
Cash and cash equivalents, end of year	$ 13,717,000				$ 13,160,000				$ 13,717,000	$ 13,160,000	$ 17,097,000