Condensed Parent Company Financial Statements (Details) - Statements of Cash Flows (Parent Company Only) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities
Net income		$ 92,349	$ 82,064	$ 69,306
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises, furniture, and equipment		12,804	13,367	12,224
Net securities gains		(1,420)	(2,373)	(8,097)
Share-based compensation expense	[1]	7,879	7,242	5,926
Tax expense related to share-based compensation		(685)	(1,200)	(106)
Net (increase) decrease in other assets		(76,902)	10,023	(18,015)
Net increase (decrease) in other liabilities		47,118	(1,042)	22,367
Investing Activities
Purchases of securities available-for-sale		(933,317)	(509,481)	(25,856)
Purchase of premises, furniture, and equipment		19,083	11,269	14,085
Net cash (used in) provided by investing activities		(1,049,338)	(496,834)	108,655
Financing Activities
Net proceeds from the issuance of subordinated debt		146,484	0	0
Payments for the retirement of senior and subordinated debt		(153,500)	0	0
Cash dividends paid		(29,198)	(27,036)	(22,568)
Restricted stock activity		(2,476)	(2,890)	(2,781)
Excess tax benefit related to share-based compensation		488	794	912
Net cash provided by (used in) financing activities		809,238	114,817	(215,578)
Net (decrease) increase in cash and cash equivalents		(119,054)	(225,060)	19,021
Cash and cash equivalents at beginning of year		381,202	606,262	587,241
Cash and cash equivalents at end of year		262,148	381,202	606,262
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		54,896	0	38,300
Parent Company
Operating Activities
Net income		92,349	82,064	69,306
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed (income) loss of subsidiaries		(25,968)	26,462	(26,280)
Depreciation of premises, furniture, and equipment		2	7	6
Net securities gains		0	(1)	(5,702)
Share-based compensation expense		7,879	7,242	5,926
Tax expense related to share-based compensation		(685)	(1,200)	(106)
Net (increase) decrease in other assets		(75,104)	23,699	4,599
Net increase (decrease) in other liabilities		74,571	(17,132)	14,063
Net cash provided by operating activities		73,044	121,141	61,812
Investing Activities
Purchases of securities available-for-sale		(14)	0	0
Proceeds from sales and maturities of securities available-for-sale		601	310	8,540
Purchase of premises, furniture, and equipment		0	5	0
Net cash paid for acquisitions		(14,905)	(16,047)	(15,809)
Net cash (used in) provided by investing activities		(14,318)	(15,742)	(7,269)
Financing Activities
Net proceeds from the issuance of subordinated debt		146,484	0	0
Payments for the retirement of senior and subordinated debt		(153,500)	0	0
Treasury stock activity		0	(120)	369
Cash dividends paid		(29,198)	(27,036)	(22,568)
Restricted stock activity		(2,476)	(2,890)	(2,781)
Excess tax benefit related to share-based compensation		488	794	912
Net cash provided by (used in) financing activities		(38,202)	(29,252)	(24,068)
Net (decrease) increase in cash and cash equivalents		20,524	76,147	30,475
Cash and cash equivalents at beginning of year		119,693	43,546	13,071
Cash and cash equivalents at end of year		140,217	119,693	43,546
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		$ 54,896	$ 0	$ 38,300

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