CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common shares par value [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Accumulated other comprehensive loss [Member]
Balance, beginning of year at Dec. 31, 2016	$ 880,970	$ 48,546	$ 0	$ 882,795	$ (50,371)
Balance, shares at Dec. 31, 2016	48,546
Net (loss) income	$ 230,155			230,155
Cash dividends ($1.20 per share)	(58,103)			(58,103)
Common shares issued	$ 16,892	558	16,334
Common shares issued, shares	558
Common shares repurchased	$ (65,000)	(924)	(13,886)	(50,190)
Common shares repurchased, shares	(924)
Other common shares retired	$ (16,596)	(227)	(16,369)
Other common shares retired, shares	(227)
Employee share-based compensation	$ 13,921		13,921
Other comprehensive income (loss)	12,774				12,774
Balance, end of year at Dec. 31, 2017	$ 1,015,013	47,953	0	1,004,657	(37,597)
Balance, shares at Dec. 31, 2017	47,953
Net (loss) income	$ 149,630			149,630
Cash dividends ($1.20 per share)	(56,743)			(56,743)
Common shares issued	$ 18,922	525	18,397
Common shares issued, shares	525
Common shares repurchased	$ (200,000)	(3,584)	(14,384)	(182,032)
Common shares repurchased, shares	(3,584)
Other common shares retired	$ (17,856)	(247)	(17,609)
Other common shares retired, shares	(247)
Employee share-based compensation	$ 13,596		13,596
Other comprehensive income (loss)	(12,115)				(12,115)
Balance, end of year at Dec. 31, 2018	$ 915,413	44,647	0	927,345	(56,579)
Balance, shares at Dec. 31, 2018	44,647
Adoption of new accounting pronouncement | Accounting Standards Update No. 2014-09 [Member]	$ 4,966			4,966
Adoption of new accounting pronouncement | Accounting Standards Update No. 2018-02 [Member]	0			6,867	(6,867)
Net (loss) income	(199,897)			(199,897)
Cash dividends ($1.20 per share)	(52,285)			(52,285)
Common shares issued	$ 3,839	194	3,645
Common shares issued, shares	194
Common shares repurchased	$ (118,547)	(2,632)	(13,615)	(102,300)
Common shares repurchased, shares	(2,632)
Other common shares retired	$ (3,935)	(83)	(3,852)
Other common shares retired, shares	(83)
Employee share-based compensation	$ 17,908		17,908
Other comprehensive income (loss)	8,632				8,632
Balance, end of year at Dec. 31, 2019	$ 570,861	$ 42,126	$ 4,086	572,596	$ (47,947)
Balance, shares at Dec. 31, 2019	42,126
Adoption of new accounting pronouncement | Accounting Standards Update No. 2016-02 [Member]	$ (267)			$ (267)