Consolidated Statements of Stockholders' Equity (unaudited) - 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, 2019	$ 497	$ 576,708	$ 696,214	$ (19,026)	$ (133,996)	$ 1,120,397
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	70,194	0	0	70,194
Cash dividends	0	0	(35,419)	0	0	(35,419)
Purchase of treasury shares	0	0	0	0	(7,980)	(7,980)
Net issuance of shares to employee and other stock plans	0	(2,928)	0	0	1,182	(1,746)
Stock-based compensation	0	3,957	0	0	0	3,957
Other comprehensive income (loss)	0	0	0	21,047	0	21,047
Balance at Sep. 30, 2020	497	577,737	726,650	2,021	(140,794)	1,166,111
Balance (ASU 2016-13 [Member]) at Sep. 30, 2020							$ 0	$ 0	$ (4,339)	$ 0	$ 0	$ (4,339)
Balance at Jun. 30, 2020	497	577,197	703,322	2,488	(140,852)	1,142,652
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	35,113	0	0	35,113
Cash dividends	0	0	(11,785)	0	0	(11,785)
Net issuance of shares to employee and other stock plans	0	(108)	0	0	58	(50)
Stock-based compensation	0	648	0	0	0	648
Other comprehensive income (loss)	0	0	0	(467)	0	(467)
Balance at Sep. 30, 2020	497	577,737	726,650	2,021	(140,794)	1,166,111
Balance (ASU 2016-13 [Member]) at Sep. 30, 2020							$ 0	$ 0	$ (4,339)	$ 0	$ 0	$ (4,339)
Balance at Dec. 31, 2020	497	578,082	749,056	417	(140,434)	1,187,618
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	117,575	0	0	117,575
Cash dividends	0	0	(35,614)	0	0	(35,614)
Purchase of treasury shares	0	0	0	0	(14,083)	(14,083)
Net issuance of shares to employee and other stock plans	0	(4,679)	0	0	1,730	(2,949)
Stock-based compensation	0	3,819	0	0	0	3,819
Other comprehensive income (loss)	0	0	0	(14,909)	0	(14,909)
Balance at Sep. 30, 2021	497	577,222	831,017	(14,492)	(152,787)	1,241,457
Balance at Jun. 30, 2021	497	576,732	805,722	(9,292)	(148,603)	1,225,056
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	37,433	0	0	37,433
Cash dividends	0	0	(12,138)	0	0	(12,138)
Purchase of treasury shares	0	0	0	0	(4,212)	(4,212)
Net issuance of shares to employee and other stock plans	0	(73)	0	0	28	(45)
Stock-based compensation	0	563	0	0	0	563
Other comprehensive income (loss)	0	0	0	(5,200)	0	(5,200)
Balance at Sep. 30, 2021	$ 497	$ 577,222	$ 831,017	$ (14,492)	$ (152,787)	$ 1,241,457