Consolidated Statements of Changes in Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance (in shares) at Dec. 31, 2016		61,031
Beginning Balance at Dec. 31, 2016	$ 960,038	$ 122,062	$ 219,955	$ 685,504	$ (67,483)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	49,796			49,796
Other comprehensive income (loss)	41,141				41,141
Dividends declared	(47,169)			(47,169)
Shares repurchased and retired (in shares)		(155)
Shares repurchased and retired	(4,997)	$ (310)		(4,687)
Share-based compensation expense, exercises and other (shares)		373
Share-based compensation expense, exercises and other	4,975	$ 747	4,228
Ending Balance (in shares) at Sep. 30, 2017		61,249
Ending Balance at Sep. 30, 2017	1,003,784	$ 122,499	224,183	683,444	(26,342)
Beginning Balance at Jun. 30, 2017					(38,926)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	10,871
Other comprehensive income (loss)	12,584
Ending Balance (in shares) at Sep. 30, 2017		61,249
Ending Balance at Sep. 30, 2017	$ 1,003,784	$ 122,499	224,183	683,444	(26,342)
Beginning Balance (in shares) at Dec. 31, 2017	61,476	61,476
Beginning Balance at Dec. 31, 2017	$ 1,015,479	$ 122,952	226,937	690,674	(25,084)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(175,191)			(175,191)
Other comprehensive income (loss)	(8,087)				(8,087)
Dividends declared	(48,357)			(48,357)
Share-based compensation expense, exercises and other (shares)		793
Share-based compensation expense, exercises and other	$ 8,569	$ 1,586	6,983
Ending Balance (in shares) at Sep. 30, 2018	62,269	62,269
Ending Balance at Sep. 30, 2018	$ 792,413	$ 124,538	233,920	467,126	(33,171)
Beginning Balance at Jun. 30, 2018					(36,203)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(565)
Other comprehensive income (loss)	$ 3,032
Ending Balance (in shares) at Sep. 30, 2018	62,269	62,269
Ending Balance at Sep. 30, 2018	$ 792,413	$ 124,538	$ 233,920	$ 467,126	$ (33,171)