Parent Company Only Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 12, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities
Net income		$ 102,953	$ 98,928	$ 62,726
Adjustments to reconcile net income to net cash provided by (used in)
Depreciation and amortization		11,879	9,556	8,615
Net security losses (gains)		(733)	1,780	(362)
Stock-based compensation		3,997	3,721	2,752
Changes in assets and liabilities:
Decrease (increase) in other assets		5,397	9,580	8,925
(Decrease) increase in other liabilities		(7,380)	2,195	(4,193)
Net cash provided by operating activities		80,800	202,547	253,358
Cash Flows from Investing Activities
Purchase of equity securities		(550)
Purchases of premises and equipment		(13,238)	(11,618)	(14,980)
Net cash provided by (used in) investing activities		64,958	(55,350)	(293,850)
Cash Flows from Financing Activities
Proceeds from charter amendment with subsidiary bank	$ 40,000
Cash paid for withholding taxes on share-based payments		(863)	(1,208)	(2,274)
Cash dividends paid		(45,171)	(39,010)	(30,707)
Proceeds from stock options exercised		169	392	906
Purchase of treasury stock		(24,292)
Common stock issuance costs		(234)		(365)
Net cash provided by (used in) financing activities		143,557	(260,496)	227,058
Net (decrease) increase in cash and due from subsidiary bank		289,315	(113,299)	186,566
Cash and cash equivalents, beginning of period		239,973	353,272	166,706
Cash and cash equivalents, ending of period		529,288	239,973	353,272
Parent
Cash Flows from Operating Activities
Net income		102,953	98,928	62,726
Adjustments to reconcile net income to net cash provided by (used in)
Depreciation and amortization		420	232	487
Distributions less than net income of subsidiaries		(51,961)	(93,451)	(69,940)
Net security losses (gains)		759	(2,322)
Stock-based compensation		3,997	3,721	2,752
Changes in assets and liabilities:
Decrease (increase) in other assets		(4,279)	13,985	(1,105)
(Decrease) increase in other liabilities		(1,280)	1,341	(2,762)
Net cash provided by operating activities		50,609	22,434	(7,842)
Cash Flows from Investing Activities
Purchase of equity securities		(520)
Net cash (outlay) received for business acquisition		(90,722)		(61,371)
Purchases of premises and equipment		(31)	(46)
Net cash provided by (used in) investing activities		(91,273)	(46)	(61,371)
Cash Flows from Financing Activities
Proceeds from charter amendment with subsidiary bank			40,000	40,000
Cash paid for withholding taxes on share-based payments		(863)	(817)	(1,414)
Cash dividends paid		(45,171)	(39,010)	(30,707)
Repayments of debt		(6,000)	(5,500)	(9,800)
Proceeds from issuance of debt		60,000		98,312
Proceeds from stock options exercised		169		626
Purchase of treasury stock		(24,292)
Common stock issuance costs		(234)		(365)
Net cash provided by (used in) financing activities		(16,391)	(5,327)	96,652
Net (decrease) increase in cash and due from subsidiary bank		(57,055)	17,061	27,439
Cash and cash equivalents, beginning of period		72,007	54,946	27,507
Cash and cash equivalents, ending of period		$ 14,952	$ 72,007	$ 54,946