Consolidated Statement Of Equity - 9 months ended Sep. 30, 2017 - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Cumulative Dividends In Excess Of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, shares at Dec. 31, 2016	39,847,860	39,847,860
Balance, value at Dec. 31, 2016	$ 1,209,590	$ 398	$ 1,173,588	$ 29,873	$ 5,731
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	121,566			121,566	(8,450)
Comprehensive income	113,116
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(1,744)		(1,744)
Stock Issued During Period, Shares, New Issues		1,660,045
Stock Issued During Period, Value, New Issues	122,198	$ 17	122,181
Shares issued on stock options exercised, shares		23,133
Adjustments Related to Tax Withholding for Share-based Compensation	(586)		(586)
Share-based compensation	2,270		2,270
Dividends declared, $1.54 per share	$ (117,177)			(117,177)
Balance, shares at Sep. 30, 2017	41,531,038	41,531,038
Balance, value at Sep. 30, 2017	$ 1,327,667	$ 415	$ 1,295,709	$ 34,262	$ (2,719)