Parent Company Financial Information (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Thousands	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
Condensed Financial Statements, Captions [Line Items]
Stock Issued									$ 0	$ 0	$ 636,385
Operating Activities
Net income	$ 46,129	$ 50,727	$ 51,724	$ 45,871	$ 44,748	$ 46,415	$ 41,749	$ 39,970	194,451	172,882	112,828
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense									9,271	8,354	7,745
Net cash provided by operating activities									204,747	237,201	128,525
Investing Activities
Net cash paid in business combinations									0	0	80,472
Net cash provided by investing activities									(865,450)	(506,083)	(199,489)
Financing Activities
Cash dividends paid									(101,911)	(83,440)	(51,308)
Repayments of Junior Subordinated Debt									0	8,248	6,186
Payments for cash settlement of acquired equity awards									0	0	(7,345)
Purchase and retirement of common stock									2,792	2,677	2,299
Purchase of treasury stock									(50,834)	0	0
Proceeds from exercise of stock options									2,025	1,857	1,980
Net cash provided by financing activities									630,789	203,936	189,259
Increase (decrease) in cash and cash equivalents									(29,914)	(64,946)	118,295
Cash and cash equivalents at beginning of period				277,587				342,533	277,587	342,533	224,238
Cash and cash equivalents at end of period	247,673				277,587				247,673	277,587	342,533
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Stock Issued									0	0	636,385
Operating Activities
Net income									194,451	172,882	112,828
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiaries									(30,089)	(91,458)	(49,656)
Stock-based compensation expense									9,271	8,354	7,745
Net changes in other assets and liabilities									(133)	1,622	1,672
Net cash provided by operating activities									173,500	91,400	72,589
Investing Activities
Net cash paid in business combinations									0	0	(580)
Net cash provided by investing activities									0	0	(580)
Financing Activities
Cash dividends paid									(102,265)	(83,459)	(51,308)
Repayments of Junior Subordinated Debt									0	8,248	6,186
Payments for cash settlement of acquired equity awards									0	0	7,345
Purchase and retirement of common stock									2,792	2,677	2,299
Purchase of treasury stock									(50,834)	0	0
Proceeds from exercise of stock options									2,025	1,857	1,980
Net cash provided by financing activities									(153,866)	(92,527)	(65,158)
Increase (decrease) in cash and cash equivalents									19,634	(1,127)	6,851
Cash and cash equivalents at beginning of period				$ 8,171				$ 9,298	8,171	9,298	2,447
Cash and cash equivalents at end of period	$ 27,805				$ 8,171				$ 27,805	$ 8,171	$ 9,298