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	35,081	0	0	35,081
Cash dividends	0	0	(23,634)	0	0	(23,634)
Purchase of treasury shares	0	0	0	0	(7,980)	(7,980)
Net issuance of shares to employee and other stock plans	0	(2,820)	0	0	1,124	(1,696)
Stock-based compensation	0	3,309	0	0	0	3,309
Other comprehensive income (loss)	0	0	0	21,514	0	21,514
Balance at Jun. 30, 2020	497	577,197	703,322	2,488	(140,852)	1,142,652
Balance (ASU 2016-13 [Member]) at Jun. 30, 2020							$ 0	$ 0	$ (4,339)	$ 0	$ 0	$ (4,339)
Balance at Mar. 31, 2020	497	577,080	678,611	(2,792)	(141,217)	1,112,179
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	24,713	0	0	24,713
Cash dividends	0	0	(2)	0	0	(2)
Net issuance of shares to employee and other stock plans	0	(517)	0	0	365	(152)
Stock-based compensation	0	634	0	0	0	634
Other comprehensive income (loss)	0	0	0	5,280	0	5,280
Balance at Jun. 30, 2020	497	577,197	703,322	2,488	(140,852)	1,142,652
Balance (ASU 2016-13 [Member]) at Jun. 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	80,142	0	0	80,142
Cash dividends	0	0	(23,476)	0	0	(23,476)
Purchase of treasury shares	0	0	0	0	(9,871)	(9,871)
Net issuance of shares to employee and other stock plans	0	(4,606)	0	0	1,702	(2,904)
Stock-based compensation	0	3,256	0	0	0	3,256
Other comprehensive income (loss)	0	0	0	(9,709)	0	(9,709)
Balance at Jun. 30, 2021	497	576,732	805,722	(9,292)	(148,603)	1,225,056
Balance at Mar. 31, 2021	497	578,597	777,170	(16,699)	(148,584)	1,190,981
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	40,296	0	0	40,296
Cash dividends	0	0	(11,744)	0	0	(11,744)
Purchase of treasury shares	0	0	0	0	(851)	(851)
Net issuance of shares to employee and other stock plans	0	(2,453)	0	0	832	(1,621)
Stock-based compensation	0	588	0	0	0	588
Other comprehensive income (loss)	0	0	0	7,407	0	7,407
Balance at Jun. 30, 2021	$ 497	$ 576,732	$ 805,722	$ (9,292)	$ (148,603)	$ 1,225,056