Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Common Stock in Treasury [Member]	Total	Cumulative Effect Adjustment for ASU Implementation [Member] Common Stock [Member]	Cumulative Effect Adjustment for ASU Implementation [Member] Additional Paid-in-Capital [Member]	Cumulative Effect Adjustment for ASU Implementation [Member] Retained Earnings [Member]	Cumulative Effect Adjustment for ASU Implementation [Member] Accumulated Other Comprehensive (Loss) Income [Member]	Cumulative Effect Adjustment for ASU Implementation [Member] Common Stock in Treasury [Member]	Cumulative Effect Adjustment for ASU Implementation [Member]
Balance at Dec. 31, 2017	$ 497	$ 574,209	$ 543,713	$ (22,077)	$ (138,165)	$ 958,177
Balance (ASU 2016-01 [Member]) at Dec. 31, 2017							$ 0	$ 0	$ 2,618	$ (2,645)	$ 0	$ (27)
Balance (ASU 2018-02 [Member]) at Dec. 31, 2017							0	0	5,575	(5,575)	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	112,566	0	0	112,566
Cash dividends	0	0	(43,269)	0	0	(43,269)
Net issuance of shares to employee and other stock plans	0	(2,679)	0	0	2,082	(597)
Stock-based compensation	0	3,936	0	0	0	3,936
Other comprehensive income (loss)	0	0	0	(12,877)	0	(12,877)
Balance at Dec. 31, 2018	497	575,466	621,203	(43,174)	(136,083)	1,017,909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	121,021	0	0	121,021
Cash dividends	0	0	(46,010)	0	0	(46,010)
Net issuance of shares to employee and other stock plans	0	(2,968)	0	0	2,087	(881)
Stock-based compensation	0	4,210	0	0	0	4,210
Other comprehensive income (loss)	0	0	0	24,148	0	24,148
Balance at Dec. 31, 2019	497	576,708	696,214	(19,026)	(133,996)	1,120,397
Balance (ASU 2016-13 [Member]) at Dec. 31, 2019							$ 0	$ 0	$ (4,339)	$ 0	$ 0	$ (4,339)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	104,388	0	0	104,388
Cash dividends	0	0	(47,207)	0	0	(47,207)
Purchase of treasury shares	0	0	0	0	(7,980)	(7,980)
Net issuance of shares to employee and other stock plans	0	(3,207)	0	0	1,542	(1,665)
Stock-based compensation	0	4,581	0	0	0	4,581
Other comprehensive income (loss)	0	0	0	19,443	0	19,443
Balance at Dec. 31, 2020	$ 497	$ 578,082	$ 749,056	$ 417	$ (140,434)	$ 1,187,618