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
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	29,127	0	0	29,127
Cash dividends	0	0	(22,774)	0	0	(22,774)
Net issuance of shares to employee and other stock plans	0	(2,099)	0	0	1,073	(1,026)
Stock-based compensation	0	2,577	0	0	0	2,577
Other comprehensive income	0	0	0	8,242	0	8,242
Balance at Mar. 31, 2019	497	575,944	627,556	(34,932)	(135,010)	1,034,055
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for ASU implementation | ASU 2016-13 [Member]	0	0	(4,339)	0	0	(4,339)
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	10,368	0	0	10,368
Cash dividends	0	0	(23,632)	0	0	(23,632)
Purchase of treasury shares	0	0	0	0	(7,980)	(7,980)
Net issuance of shares to employee and other stock plans	0	(2,303)	0	0	759	(1,544)
Stock-based compensation	0	2,675	0	0	0	2,675
Other comprehensive income	0	0	0	16,234	0	16,234
Balance at Mar. 31, 2020	$ 497	$ 577,080	$ 678,611	$ (2,792)	$ (141,217)	$ 1,112,179