Parent Company Only Financial Information (Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 32,141	$ 33,710	$ 27,879	$ 23,268	$ 13,672	$ 21,632	$ 21,958	$ 18,010	$ 116,998	$ 75,272	$ 80,349
Adjustments to reconcile net income to net cash provided by operating activities:
Securities gains, net									(1,085)	(6,973)	(11,340)
Gain on extinguishment of debt									0	(1,280)	0
Other, net									(8,760)	(14,148)	(6,769)
NET CASH PROVIDED BY OPERATING ACTIVITIES									242,750	155,930	148,525
Cash flows from investing activities:
Proceeds from sales of available for sale securities									727,895	1,456,750	909,942
Net assets acquired									212,197	71,089	8,084
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES									(124,220)	27,298	6,855
Cash flows from financing activities:
Proceeds on short-term revolving credit line									25,000	20,000	0
Proceeds from other borrowings									30,131	0	40,000
Repayments on short-term revolving credit line									(25,000)	(20,000)	0
Repayments of other borrowings									(59,157)	(9,645)	(21,636)
Payment for the redemption of debt									0	(13,800)	0
Redemption of preferred stock									0	0	(81,698)
Cash dividends paid									(19,357)	(14,557)	(12,870)
Purchase of treasury stock									(97)	(625)	(3,719)
Proceeds from issuance of common stock									489	963	54,196
NET CASH USED BY FINANCING ACTIVITIES									(40,903)	(145,949)	(255,455)
Net increase (decrease) in cash and cash equivalents									77,627	37,279	(100,075)
Cash and cash equivalents at beginning of year				196,003				158,724	196,003	158,724	258,799
CASH AND CASH EQUIVALENTS AT END OF PERIOD	273,630				196,003				273,630	196,003	158,724
Supplemental disclosure:
Conversion of convertible debt to common stock									0	558	1,442
Conversion/redemption of Series D preferred stock to common stock									938	419	2,420
Stock consideration granted for acquisitions									238,075	175,196	57,433
Parent
Cash flows from operating activities:
Net income									116,998	75,272	80,349
Adjustments to reconcile net income to net cash provided by operating activities:
Undistributed earnings of subsidiaries									(52,570)	(16,212)	(37,926)
Securities gains, net									0	(3,021)	(54)
Gain on extinguishment of debt									0	(1,200)	0
Increase (decrease) in accrued expenses and other liabilities									5,336	(4,160)	(7,039)
(Increase) decrease in other assets									(1,559)	(567)	1,948
Excess tax benefits from stock based compensation									674	1,246	374
Other, net									5,401	4,714	4,892
NET CASH PROVIDED BY OPERATING ACTIVITIES									74,280	56,072	42,544
Cash flows from investing activities:
Capital contributions to subsidiaries									(30,696)	0	(18,000)
Proceeds from sales of available for sale securities									0	2,868	0
Proceeds from the sale, maturity of and principal paydowns on other investments									0	211	94
Net assets acquired									(13,504)	(62,813)	(14,587)
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES									(44,200)	(59,734)	(32,493)
Cash flows from financing activities:
Proceeds on short-term revolving credit line									25,000	20,000	0
Proceeds from other borrowings									30,000	0	40,000
Repayments on short-term revolving credit line									(25,000)	(20,000)	0
Repayments of other borrowings									(25,759)	(9,016)	(26,280)
Payment for the redemption of debt									0	(13,800)	0
Redemption of preferred stock									0	0	(81,698)
Cash dividends paid									(19,357)	(14,557)	(12,870)
Purchase of treasury stock									(97)	(625)	(3,719)
Proceeds from issuance of common stock									489	963	54,196
NET CASH USED BY FINANCING ACTIVITIES									(14,724)	(37,035)	(30,371)
Net increase (decrease) in cash and cash equivalents									15,356	(40,697)	(20,320)
Cash and cash equivalents at beginning of year				$ 24,310				$ 65,007	24,310	65,007	85,327
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$ 39,666				$ 24,310				39,666	24,310	65,007
Supplemental disclosure:
Conversion of convertible debt to common stock									0	558	1,442
Conversion/redemption of Series D preferred stock to common stock									938	419	2,420
Stock consideration granted for acquisitions									$ 238,075	$ 175,196	$ 57,433