Condensed Parent Company Financial Statements - Statements of Cash Flows (Parent Company Only) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net income		$ 157,870	$ 98,387	$ 92,349
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises, furniture, and equipment		15,865	13,995	12,804
Net securities losses		0
Net securities losses			1,876	(1,420)
Share-based compensation expense	[1]	12,062	11,223	7,879
Tax benefit (expense) related to share-based compensation		258	349	(197)
Net decrease (increase) in other assets		(44,246)	121,577	(76,902)
Net (decrease) increase in other liabilities		(4,346)	(56,055)	47,315
Net cash provided by operating activities		253,184	234,266	121,731
Investing Activities
Purchases of premises, furniture, and equipment		(27,800)	(16,123)	(19,083)
Net cash used in investing activities		(1,002,386)	(145,780)	(1,049,338)
Financing Activities
Net proceeds from the issuance of subordinated debt		0	0	146,484
Payments for the retirement of senior and subordinated debt		0	0	(153,500)
Cash dividends paid		(44,293)	(37,129)	(29,198)
Restricted stock activity		(4,421)	(3,659)	(2,673)
Net cash provided by (used in) financing activities		691,890	(4,064)	808,553
Net (decrease) increase in cash and cash equivalents		(57,312)	84,422	(119,054)
Cash and cash equivalents at beginning of year		346,570	262,148	381,202
Cash and cash equivalents at end of year		289,258	346,570	262,148
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		83,303	534,090	54,896
Parent Company
Operating Activities
Net income		157,870	98,387	92,349
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed income of subsidiaries		(102,321)	(51,138)	(25,968)
Depreciation of premises, furniture, and equipment		42	9	2
Net securities losses		0
Net securities losses			1,523	0
Share-based compensation expense		12,062	11,223	7,879
Tax benefit (expense) related to share-based compensation		258	349	(197)
Net decrease (increase) in other assets		35,981	18,667	(75,104)
Net (decrease) increase in other liabilities		(17,942)	(52,377)	74,571
Net cash provided by operating activities		85,950	26,643	73,532
Investing Activities
Purchases of securities available-for-sale		0	0	(14)
Proceeds from sales and maturities of securities available-for-sale		0	42,516	601
Purchases of premises, furniture, and equipment		(61)	(119)	0
Net cash received (paid) for acquisitions		39	(47,364)	(14,905)
Net cash used in investing activities		(22)	(4,967)	(14,318)
Financing Activities
Net proceeds from the issuance of subordinated debt		0	0	146,484
Payments for the retirement of senior and subordinated debt		0	0	(153,500)
Cash dividends paid		(44,293)	(37,129)	(29,198)
Restricted stock activity		(4,421)	(3,952)	(2,476)
Net cash provided by (used in) financing activities		(48,714)	(41,081)	(38,690)
Net (decrease) increase in cash and cash equivalents		37,214	(19,405)	20,524
Cash and cash equivalents at beginning of year		120,812	140,217	119,693
Cash and cash equivalents at end of year		158,026	120,812	140,217
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		$ 83,303	$ 534,090	$ 54,896

[1] Comprised of restricted stock, restricted stock unit, and performance share awards expense.