Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common stock	Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Accumulated Other Comprehensive Earnings (Loss) Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Deferred Compensation	Treasury Stock at Cost
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	$ 806,842		$ 674	$ 305,660	$ (14,572)		$ 908,079		$ 8,354	$ (401,353)
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	2,892		$ 1	2,891
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	894,705		$ 675	308,551	14,729		963,749		7,315	(400,314)
Shares, Outstanding, Ending Balance at Mar. 31, 2019			44,554,256
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	806,842		$ 674	305,660	(14,572)		908,079		8,354	(401,353)
Shares, Outstanding, Beginning Balance at Dec. 31, 2018			44,504,043
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)	138,264
Other comprehensive earnings (loss), net of tax	72,506
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	999,620		$ 678	318,092	57,934		1,015,915		7,788	(400,787)
Shares, Outstanding, Ending Balance at Sep. 30, 2019			44,832,088
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2019	894,705		$ 675	308,551	14,729		963,749		7,315	(400,314)
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	7,217		$ 2	7,215
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	959,948		$ 677	315,766	42,593		993,911		7,530	(400,529)
Shares, Outstanding, Ending Balance at Jun. 30, 2019			44,787,197
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)	32,324						32,324
Other comprehensive earnings (loss), net of tax	15,341				15,341
Deferred compensation									258	(258)
Share-based compensation	2,327		$ 1	2,326
Share-based compensation (in shares)			44,891
Dividends and dividend equivalents	(10,320)						(10,320)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	999,620		$ 678	318,092	57,934		1,015,915		7,788	(400,787)
Shares, Outstanding, Ending Balance at Sep. 30, 2019			44,832,088
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2019	$ 995,388	$ 1,095	$ 678	321,190	52,473	$ 22	1,014,046	$ 1,073	7,980	(400,979)
Shares, Outstanding, Beginning Balance at Dec. 31, 2019			44,869,015
Increase (Decrease) in Shareholders' Equity
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
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	3,863		$ 1	3,862
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	915,705		$ 679	325,052	39,464		943,509		6,970	(399,969)
Shares, Outstanding, Ending Balance at Mar. 31, 2020			44,922,656
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2019	995,388	$ 1,095	$ 678	321,190	52,473	$ 22	1,014,046	$ 1,073	7,980	(400,979)
Shares, Outstanding, Beginning Balance at Dec. 31, 2019			44,869,015
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)	73,286
Other comprehensive earnings (loss), net of tax	50,090
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2020	1,099,340		$ 680	332,629	102,585		1,056,445		7,703	(400,702)
Shares, Outstanding, Ending Balance at Sep. 30, 2020			45,055,164
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2020	915,705		$ 679	325,052	39,464		943,509		6,970	(399,969)
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	1,051,458		$ 679	325,862	93,035		1,024,881		7,600	(400,599)
Shares, Outstanding, Ending Balance at Jun. 30, 2020			44,952,602
Increase (Decrease) in Shareholders' Equity
Net earnings (loss)	42,387						42,387
Other comprehensive earnings (loss), net of tax	9,550				9,550
Deferred compensation									103	(103)
Share-based compensation	6,768		$ 1	6,767
Share-based compensation (in shares)			102,562
Dividends and dividend equivalents	(10,823)						(10,823)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2020	$ 1,099,340		$ 680	$ 332,629	$ 102,585		$ 1,056,445		$ 7,703	$ (400,702)
Shares, Outstanding, Ending Balance at Sep. 30, 2020			45,055,164