Consolidated Statements Of Changes In Equity (Unaudited) - Class of Stock [Domain] - USD ($) shares in Thousands, $ in Thousands		Total	Common Shares Outstanding [Member]	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]		Accumulated Other Comprehensive Income [Member]
Beginning Balance (in shares) at Dec. 31, 2013			77,707
Beginning Balance at Dec. 31, 2013		$ 1,301,904		$ 76,825	$ (6,415)	$ 1,022,023	$ 199,627		$ 9,844
Comprehensive income (loss)
Net income (loss)		75,329					75,329	[1]
Other comprehensive income (loss)		13,562							13,562	[1]
Total comprehensive income (loss)	[1]	88,891
Cash dividends declared:
Cash dividends declared ($0.01 per common share)		(1,576)					(1,576)
Common stock issued for: [Abstract]
Nonvested (restricted) stock grants, shares			374
Nonvested (restricted) stock grants		0		(242)	5,548	(5,306)
Exercise of stock options, shares			154
Exercise of stock options		3,054		0	4,429	(1,375)
Restricted stock activity		0		528	360	(888)
Deferred compensation plan, shares			13
Deferred compensation plan		384		0	384	0
Excess tax benefit from share-based compensation plans		2,838				2,838
Stock repurchased in connection with share-based compensation plans, shares			(179)
Stock repurchased in connection with share-based compensation plans		(5,251)			(5,251)
Share-based compensation expense		7,577				7,577
Ending Balance (in shares) at Jun. 30, 2014			78,069
Ending Balance at Jun. 30, 2014		1,397,821		77,111	(945)	1,024,869	273,380		23,406
Beginning Balance (in shares) at Dec. 31, 2014			78,178
Beginning Balance at Dec. 31, 2014		1,481,679		77,211	(53)	1,034,048	349,556		20,917
Comprehensive income (loss)
Net income (loss)		87,906					87,906	[1]
Other comprehensive income (loss)		(1,789)							(1,789)	[1]
Total comprehensive income (loss)	[1]	86,117
Cash dividends declared:
Cash dividends declared ($0.01 per common share)		(1,590)					(1,590)
Common stock issued for: [Abstract]
Nonvested (restricted) stock grants, shares			250
Nonvested (restricted) stock grants		0		0	0	0
Exercise of stock options, shares			451
Exercise of stock options		10,857		281	5,903	4,673
Restricted stock activity, shares			7
Restricted stock activity		0		555	0	(555)
Deferred compensation plan, shares			1
Deferred compensation plan		226			29	197
Excess tax benefit from share-based compensation plans		3,956				3,956
Stock repurchased in connection with share-based compensation plans, shares			(170)
Stock repurchased in connection with share-based compensation plans		(5,908)			(5,908)
Share-based compensation expense		9,459				9,459
Ending Balance (in shares) at Jun. 30, 2015			78,717
Ending Balance at Jun. 30, 2015		$ 1,584,796		$ 78,047	$ (29)	$ 1,051,778	$ 435,872		$ 19,128

[1] Net of taxes and reclassification adjustments.