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, 2018	$ 497	$ 575,466	$ 621,203	$ (43,174)	$ (136,083)	$ 1,017,909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	59,682	0	0	59,682
Cash dividends	0	0	(22,778)	0	0	(22,778)
Net issuance of shares to employee and other stock plans	0	(2,812)	0	0	1,544	(1,268)
Stock-based compensation	0	3,140	0	0	0	3,140
Other comprehensive income	0	0	0	18,138	0	18,138
Balance at Jun. 30, 2019	497	575,794	658,107	(25,036)	(134,539)	1,074,823
Balance at Mar. 31, 2019	497	575,944	627,556	(34,932)	(135,010)	1,034,055
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	30,555	0	0	30,555
Cash dividends	0	0	(4)	0	0	(4)
Net issuance of shares to employee and other stock plans	0	(713)	0	0	471	(242)
Stock-based compensation	0	563	0	0	0	563
Other comprehensive income	0	0	0	9,896	0	9,896
Balance at Jun. 30, 2019	497	575,794	658,107	(25,036)	(134,539)	1,074,823
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	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	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 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	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