Consolidated Statement Of Equity - 6 months ended Jun. 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	82,475			82,475	(8,855)
Comprehensive income	73,620
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(337)		(337)
Stock Issued During Period, Shares, New Issues		1,123,184
Stock Issued During Period, Value, New Issues	79,772	$ 12	79,760
Shares issued on stock options exercised, shares		13,245
Adjustments Related to Tax Withholding for Share-based Compensation	(360)		(360)
Share-based compensation	1,865		1,865
Dividends declared, $1.54 per share	$ (77,724)			(77,724)
Balance, shares at Jun. 30, 2017	40,984,289	40,984,289
Balance, value at Jun. 30, 2017	$ 1,286,426	$ 410	$ 1,254,516	$ 34,624	$ (3,124)