CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Treasury Stock	Paid-In Capital	Accumulated Other Comprehensive Income / (Loss)	Retained Earnings
Balance at Dec. 31, 2010	$ 1,872,700	$ 41,684	$ (3,349)	$ 689,657	$ (3,683)	$ 1,148,391
Balance (in shares) at Dec. 31, 2010		416,840	808
Increase (Decrease) in Stockholders' Equity
Net income	122,408					122,408
Exercise of stock options and stock appreciation rights	(1,746)	32		(1,778)
Exercise of stock options and stock appreciation rights (in shares)		319
Stock amortization and vesting	13,950	88		13,862
Stock amortization and vesting (in shares)		880
Sale of stock held in rabbi trust	1,734			1,734
Cash dividends at $0.06, $0.04 and $0.03 per share for the year ended December 31, 2013, 2012 and 2011, respectively	(12,508)					(12,508)
Other comprehensive income / (loss)	108,230				108,230
Balance at Dec. 31, 2011	2,104,768	41,804	(3,349)	703,475	104,547	1,258,291
Balance (in shares) at Dec. 31, 2011		418,039	808
Increase (Decrease) in Stockholders' Equity
Net income	131,730					131,730
Exercise of stock options and stock appreciation rights	(6,708)	44		(6,752)
Exercise of stock options and stock appreciation rights (in shares)		438
Stock amortization and vesting	(919)	238		(1,157)
Stock amortization and vesting (in shares)		2,384
Cash dividends at $0.06, $0.04 and $0.03 per share for the year ended December 31, 2013, 2012 and 2011, respectively	(16,757)					(16,757)
Other comprehensive income / (loss)	(80,667)				(80,667)
Balance at Dec. 31, 2012	2,131,447	42,086	(3,349)	695,566	23,880	1,373,264
Balance (in shares) at Dec. 31, 2012		420,861	808
Increase (Decrease) in Stockholders' Equity
Net income	279,773					279,773
Exercise of stock options and stock appreciation rights	(13,226)	38		(13,264)
Exercise of stock options and stock appreciation rights (in shares)		382
Stock amortization and vesting	9,802	77		9,725
Stock amortization and vesting (in shares)		772
Tax benefit of stock-based compensation	18,913			18,913
Purchase of treasury stock	(164,634)		(164,634)
Purchase of treasury stock (in shares)	4,800		4,810
Cash dividends at $0.06, $0.04 and $0.03 per share for the year ended December 31, 2013, 2012 and 2011, respectively	(25,232)					(25,232)
Other comprehensive income / (loss)	(32,241)				(32,241)
Balance at Dec. 31, 2013	$ 2,204,602	$ 42,201	$ (167,983)	$ 710,940	$ (8,361)	$ 1,627,805
Balance (in shares) at Dec. 31, 2013		422,015	5,618