Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 112,633	$ 118,387	$ 93,949
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of intangibles	10,395	10,101	11,623
Provision for loan losses	13,100	23,700	5,600
Deferred tax expense (benefit)	1,674	(18,541)	40,634
Amortization of operating lease right-of-use assets	8,433
Income on Bank-owned life insurance	(6,297)	(5,514)	(6,693)
Net amortization of premiums and discounts on securities	7,789	8,540	9,948
Accretion of net deferred loan fees	(5,643)	(5,773)	(4,655)
Amortization of premiums on purchased loans, net	845	894	1,021
Net increase in loans originated for sale	(16,212)	(36,043)	(24,938)
Proceeds from sales of loans originated for sale	17,202	37,386	26,387
Proceeds from sales and paydowns of foreclosed assets	1,354	7,963	5,423
ESOP expense	4,533	4,516	4,600
Allocation of stock award shares	6,671	6,046	4,963
Allocation of stock options	181	190	203
Net gain on sale of loans	(990)	(1,343)	(1,449)
Net gain on securities transactions	(72)	(2,221)	(57)
Net gain on sale of premises and equipment	0	(25)	(20)
Net gain on sale of foreclosed assets	(190)	(798)	(819)
Decrease (increase) in accrued interest receivable	2,444	(1,829)	(2,564)
(Increase) decrease in other assets	(46,237)	5,266	(52,078)
Increase in other liabilities	25,312	4,817	6,142
Net cash provided by operating activities	136,925	155,719	117,220
Cash flows from investing activities:
Proceeds from maturities, calls and paydowns of held to maturity debt securities	42,696	39,534	55,720
Purchases of held to maturity debt securities	(20,303)	(43,887)	(47,894)
Proceeds from sales of available for sale debt securities	0	2,212	0
Proceeds from maturities, calls and paydowns of available for sale debt securities	223,806	196,690	220,138
Purchases of available for sale debt securities	(117,022)	(237,076)	(228,363)
Proceeds from redemption of Federal Home Loan Bank stock	172,293	145,191	130,125
Purchases of Federal Home Loan Bank stock	(160,778)	(132,820)	(135,583)
BOLI claim benefits received	1,891	1,954	4,428
Net cash paid in acquisition	(15,022)	0	0
Purchases of loans	0	(1,344)	0
Net (increase) decrease in loans	(79,812)	79,388	(322,443)
Proceeds from sales of premises and equipment	0	25	20,766
Purchases of premises and equipment	(4,882)	(3,162)	(3,231)
Net cash provided by (used in) investing activities	42,867	46,705	(306,337)
Cash flows from financing activities:
Net increase in deposits	272,487	115,956	160,537
Increase (decrease) in mortgage escrow deposits	1,236	(365)	1,481
Purchase of treasury stock	(19,867)	(13,172)	(443)
Purchase of employee restricted shares to fund statutory tax withholding	(1,985)	(1,896)	(778)
Cash dividends paid to stockholders	(72,809)	(53,604)	(59,980)
Shares issued to dividend reinvestment plan	2,230	1,709	2,114
Stock options exercised	139	1,007	2,954
Proceeds from long-term borrowings	1,243,000	695,000	347,000
Payments on long-term borrowings	(1,549,551)	(804,375)	(539,745)
Net (decrease) increase in short-term borrowings	(10,585)	(190,857)	322,514
Net cash (used in) provided by financing activities	(135,705)	(250,597)	235,654
Net increase (decrease) in cash and cash equivalents	44,087	(48,173)	46,537
Cash and cash equivalents at beginning of period	142,661	190,834	144,297
Cash and cash equivalents at end of period	186,748	142,661	190,834
Cash paid during the period for:
Interest on deposits and borrowings	73,664	58,959	46,391
Income taxes	34,494	15,259	40,566
Non cash investing activities:
Initial recognition of operating lease right-of-use assets	44,946
Initial recognition of operating lease liabilities	46,050
Transfer of loans receivable to foreclosed assets	2,314	1,965	3,845
Non-Cash Assets Acquired [Abstract]
Goodwill and other intangible assets, net	21,562	0	0
Other assets	71	0	0
Total non-cash assets acquired	$ 21,633	$ 0	$ 0