Consolidated Statements Of Changes in Shareholders Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at beginning of period at Dec. 31, 2011	$ 903,667	$ 675	$ 355,628	$ 0	$ 601,282	$ (53,918)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	108,292				108,292
Other comprehensive income, net of tax	3,543					3,543
Stock options exercised	966		966
Common stock shares withheld to satisfy employee tax obligations	(11,379)	(1)	(11,378)
Restricted stock units vested, net	0	3	(3)
Amortization of share-based payment expense	19,240		19,240
Net tax benefit associated with the vesting or exercise of share-based payments	2,792		2,792
Shares and deferred stock units issued to directors	928		928
Cash dividends, (2012: $0.52, 2013: $0.20, 2014: $4.74) per common share	(35,223)				(35,223)
Balance at end of period at Dec. 31, 2012	992,826	677	368,173	0	674,351	(50,375)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	130,006				130,006
Other comprehensive income, net of tax	10,922					10,922
Stock options exercised	4,049	2	4,047
Warrants exercised	0	7	(7)
Common stock shares withheld to satisfy employee tax obligations	(11,399)		(11,399)
Restricted stock units vested, net	0	4	(4)
Amortization of share-based payment expense	22,350		22,350
Net tax benefit associated with the vesting or exercise of share-based payments	3,521		3,521
Shares and deferred stock units issued to directors	797	1	796
Cash dividends, (2012: $0.52, 2013: $0.20, 2014: $4.74) per common share	(13,754)				(13,754)
Balance at end of period at Dec. 31, 2013	1,139,318	691	387,477	0	790,603	(39,453)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	117,795				117,795
Other comprehensive income, net of tax	(37,313)					(37,313)
Stock options exercised	967		967
Common stock shares withheld to satisfy employee tax obligations	(11,848)		(11,848)
Restricted stock units vested, net	0	4	(4)
Amortization of share-based payment expense	27,061		27,061
Net tax benefit associated with the vesting or exercise of share-based payments	3,625		3,625
Shares and deferred stock units issued to directors	1,596		1,596
Treasury Stock, Retired, Cost Method, Amount	(25,000)			(25,000)
Cash dividends, (2012: $0.52, 2013: $0.20, 2014: $4.74) per common share	(327,754)				(327,754)
Cash dividend equivalents paid on share-based payments	(3,781)				(3,781)
Cash dividend equivalents accrued on share-based payments	(6,969)				(6,969)
Balance at end of period at Dec. 31, 2014	$ 877,697	$ 695	$ 408,874	$ (25,000)	$ 569,894	$ (76,766)