Consolidated Statements of Changes in Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Shares, Outstanding		73,249
Adjustment to opening retained earnings pursuant to adoption of ASU | Accounting Standards Update 2016-01 [Member]	$ 782		$ 782
Common Stock, Dividends, Per Share, Cash Paid	$ 0.42
Balance, value at Dec. 31, 2018	$ 2,033,649	$ 1,642,246	426,708	$ (35,305)
Net income	45,871		45,871
Other comprehensive income (loss)	38,351			38,351
Issuance of common stock - stock option and other plans, shares		25
Issuance of common stock - stock option and other plans, value	878	$ 878
Issuance of common stock - restricted stock awards, net of canceled awards, shares		355
Issuance of common stock - restricted stock awards, net of canceled awards, value	2,285	$ 2,285
Purchase and retirement of common stock, Shares		(64)
Purchase and retirement of common stock, Value	(2,432)	$ (2,432)
Cash dividends declared on common stock	(30,764)		(30,764)
Balance, value at Mar. 31, 2019	2,088,620	$ 1,642,977	442,597	3,046	$ 0
Shares, Outstanding		73,565
Shares, Outstanding		72,124
Adjustment to opening retained earnings pursuant to adoption of ASU | Accounting Standards Update 2016-02 [Member]	$ (2,457)		(2,457)
Common Stock, Dividends, Per Share, Cash Paid	$ 0.50
Balance, value at Dec. 31, 2019	$ 2,159,962	$ 1,650,753	519,676	40,367	(50,834)
Net income	14,628		14,628
Other comprehensive income (loss)	96,840			96,840
Issuance of common stock - stock option and other plans, shares		26
Issuance of common stock - stock option and other plans, value	945	$ 945
Stock Adjustment Deferred Compensation - Shares		0
Stock Adjustment Value Deferred Compensation	3	$ 3
Issuance of common stock - restricted stock awards, net of canceled awards, shares		222
Issuance of common stock - restricted stock awards, net of canceled awards, value	2,172	$ 2,172
Purchase and retirement of common stock, Shares		66
Purchase and retirement of common stock, Value	(2,474)	$ (2,474)
Cash dividends declared on common stock	$ (36,017)		(36,017)
Purchase of treasury stock, Shares	(731)	(731)
Purchase of treasury stock, value	$ (20,000)				20,000
Balance, value at Mar. 31, 2020	$ 2,213,602	$ 1,651,399	$ 495,830	$ 137,207	$ (70,834)
Shares, Outstanding		71,575