CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Cash Flows from Operating Activities
Net income			$ 73,638	$ 50,433
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based and non-cash compensation			2,666	1,935
Depreciation			7,158	6,084
Amortization of intangible assets	$ 1,445	$ 1,286	4,450	3,675
Premises and equipment impairment			817
Provision for loan losses	758	1,494	4,024	2,494
Provision for deferred income taxes			4,696	(3,480)
Amortization of security premiums and discounts, net			6,545	4,172
Accretion of premiums and discounts on time deposits and trust preferred securities, net			(82)	(232)
Accretion of premiums and discounts on portfolio loans, net			(8,615)	(6,329)
Security gains, net		(290)	(160)	(1,143)
Change in equity securities, net			(2,699)
Gain on sales of mortgage loans, net of origination costs			(7,805)	(36,911)
Mortgage loans originated for sale			(336,169)	(1,166,083)
Proceeds from sales of mortgage loans			406,205	1,314,779
Net losses (gains) on disposition of premises and equipment			186	(57)
Increase in cash surrender value of bank owned life insurance			(926)	(1,604)
Change in assets and liabilities:
(Increase) decrease in other assets			(3,627)	14,049
Decrease in other liabilities			(7,215)	(5,513)
Increase in interest payable			1,849	1,650
Decrease in income taxes receivable			2,200	1,435
Net cash provided by operating activities			147,136	179,354
Cash Flows from Investing Activities
Proceeds from sales of securities classified available for sale				134,515
Proceeds from sales of securities classified equity			920
Proceeds from maturities of securities classified available for sale			115,522	154,435
Proceeds from sales of securities classified held to maturity			31,815
Proceeds from maturities of securities classified held to maturity				6,358
Purchase of securities classified available for sale			(122,954)	(128,425)
Purchase of securities classified held to maturity			(217,767)	(185,201)
Net increase in loans			(104,195)	(98,040)
Proceeds from disposition of premises and equipment			26	622
Proceeds from sale of other real estate owned (“OREO”) properties			4,275	4,069	$ 5,024
Purchases of premises and equipment			(10,436)	(11,336)
Proceeds (purchases) from the redemption of Federal Home Loan Bank ("FHLB") stock, net			(2,611)	4,322
Net cash received in acquisitions				29,947
Net cash used in investing activities			(305,405)	(88,734)
Cash Flows from Financing Activities
Net increase (decrease) in certificates of deposit			216,313	(92,596)
Net increase in demand deposits, money market and savings accounts			(146,517)	(42,414)
Net increase (decrease) in federal funds purchased and securities sold under agreements to repurchase			(48,660)	4,443
Proceeds from short-term borrowings, net				53,150
Repayment of long-term advances			(5,500)	(39,800)
Net proceeds from issuance of senior debt				39,326
Net proceeds from issuance of subordinated debt				58,986
Cash dividends paid			(29,238)	(21,971)
Proceeds from FHLB long term advances, net			(20,000)
Value of shares surrendered upon vesting to satisfy tax withholding obligations of stock-based compensation			(1,136)	(1,975)
Proceeds from stock options exercised			387	165
Common stock issuance costs				(259)
Net cash (used in) financing activities			(34,351)	(42,945)
Net increase (decrease) in cash and cash equivalents			(192,620)	47,675
Cash and cash equivalents, beginning of period			353,272	166,706	166,706
Cash and cash equivalents, ending of period	$ 160,652	$ 214,381	160,652	214,381	$ 353,272
Cash payments for:
Interest			26,665	11,485
Income taxes			20,127	19,369
Non-cash Investing and Financing Activities:
Other real estate acquired in settlement of loans			$ 3,706	$ 477