Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common stock	Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Retained Earnings	Deferred Compensation	Treasury Stock at Cost	Total
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	$ 674	$ 305,660	$ (14,572)	$ 908,079	$ 8,354	$ (401,353)	$ 806,842
Common Stock, Shares, Outstanding, Beginning Balance at Dec. 31, 2018	44,504,043
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)				65,473			65,473
Other comprehensive earnings (loss), net of tax			29,301				29,301
Deferred compensation					(1,039)	1,039
Share-based compensation	$ 1	2,891					2,892
Share-based compensation (in shares)	50,213
Dividends and dividend equivalents				(9,803)			(9,803)
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2019	$ 675	308,551	14,729	963,749	7,315	(400,314)	894,705
Common Stock, Shares, Outstanding, Ending Balance at Mar. 31, 2019	44,554,256
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	$ 674	305,660	(14,572)	908,079	8,354	(401,353)	806,842
Common Stock, Shares, Outstanding, Beginning Balance at Dec. 31, 2018	44,504,043
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)							105,940
Other comprehensive earnings (loss), net of tax							57,165
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2019	$ 677	315,766	42,593	993,911	7,530	(400,529)	959,948
Common Stock, Shares, Outstanding, Ending Balance at Jun. 30, 2019	44,787,197
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2019	$ 675	308,551	14,729	963,749	7,315	(400,314)	894,705
Common Stock, Shares, Outstanding, Beginning Balance at Mar. 31, 2019	44,554,256
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)				40,467			40,467
Other comprehensive earnings (loss), net of tax			27,864				27,864
Deferred compensation					215	(215)
Share-based compensation	$ 2	7,215					7,217
Share-based compensation (in shares)	232,941
Dividends and dividend equivalents				(10,305)			(10,305)
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2019	$ 677	315,766	42,593	993,911	7,530	(400,529)	959,948
Common Stock, Shares, Outstanding, Ending Balance at Jun. 30, 2019	44,787,197
Increase (Decrease) in Shareholders' Equity
Cumulative-effect adjustment from ASU 2016-13			22	1,073			1,095
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2019	$ 678	321,190	52,473	1,014,046	7,980	(400,979)	$ 995,388
Common Stock, Shares, Outstanding, Beginning Balance at Dec. 31, 2019	44,869,015						44,869,015
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)				(61,267)			$ (61,267)
Other comprehensive earnings (loss), net of tax			(13,031)				(13,031)
Deferred compensation					(1,010)	1,010
Share-based compensation	$ 1	3,862					3,863
Share-based compensation (in shares)	53,641
Dividends and dividend equivalents				(10,343)			(10,343)
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2020	$ 679	325,052	39,464	943,509	6,970	(399,969)	915,705
Common Stock, Shares, Outstanding, Ending Balance at Mar. 31, 2020	44,922,656
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2019	$ 678	321,190	52,473	1,014,046	7,980	(400,979)	$ 995,388
Common Stock, Shares, Outstanding, Beginning Balance at Dec. 31, 2019	44,869,015						44,869,015
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)							$ 30,899
Other comprehensive earnings (loss), net of tax							40,540
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2020	$ 679	325,862	93,035	1,024,881	7,600	(400,599)	$ 1,051,458
Common Stock, Shares, Outstanding, Ending Balance at Jun. 30, 2020	44,952,602						44,952,602
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2020	$ 679	325,052	39,464	943,509	6,970	(399,969)	$ 915,705
Common Stock, Shares, Outstanding, Beginning Balance at Mar. 31, 2020	44,922,656
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)				92,166			92,166
Other comprehensive earnings (loss), net of tax			53,571				53,571
Deferred compensation					630	(630)
Share-based compensation		810					810
Share-based compensation (in shares)	29,946
Dividends and dividend equivalents				(10,794)			(10,794)
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2020	$ 679	$ 325,862	$ 93,035	$ 1,024,881	$ 7,600	$ (400,599)	$ 1,051,458
Common Stock, Shares, Outstanding, Ending Balance at Jun. 30, 2020	44,952,602						44,952,602