Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total		Common stock [Member]	Additional paid-in capital [Member]	Retained earnings [Member]
Balance at Dec. 31, 2012	$ 2,108,307		$ 1,130	$ 1,083,910	$ 1,023,267
Balance (in shares) at Dec. 31, 2012			112,963,000
Net income	670,292				670,292
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes	10,663		$ 0	10,663
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares			113,000
Net issuance of common stock upon exercise of stock options	59,745		$ 14	59,731
Net issuance of common stock upon exercise of stock options, shares			1,393,000
Excess tax benefit from share-based compensation	30,811			30,811
Share based compensation	19,531			19,531
Share repurchases, including fees	(933,028)		$ (85)	(85,717)	(847,226)
Share repurchases, shares			(8,529,000)
Balance at Dec. 31, 2013	1,966,321		$ 1,059	1,118,929	846,333
Balance (in shares) at Dec. 31, 2013			105,940,000
Net income	778,182				778,182
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes	11,181		$ 1	11,180
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares			86,000
Net issuance of common stock upon exercise of stock options	59,594		$ 13	59,581
Net issuance of common stock upon exercise of stock options, shares			1,320,000
Excess tax benefit from share-based compensation	49,150			49,150
Share based compensation	20,474			20,474
Share repurchases, including fees	$ (866,484)		$ (57)	(64,385)	(802,042)
Share repurchases, shares	(5,743,000)		(5,743,000)
Balance at Dec. 31, 2014	$ 2,018,418	[1]	$ 1,016	1,194,929	822,473
Balance (in shares) at Dec. 31, 2014	101,602,935		101,603,000
Net income	$ 931,216				931,216
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes	11,630			11,630
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares			59,000
Net issuance of common stock upon exercise of stock options	52,911		$ 10	52,901
Net issuance of common stock upon exercise of stock options, shares			976,000
Excess tax benefit from share-based compensation	63,078			63,078
Share based compensation	20,274			20,274
Share repurchases, including fees	$ (1,136,213)		$ (49)	(61,315)	(1,074,849)
Share repurchases, shares	(4,901,000)		(4,901,000)
Balance at Dec. 31, 2015	$ 1,961,314		$ 977	$ 1,281,497	$ 678,840
Balance (in shares) at Dec. 31, 2015	97,737,171		97,737,000

[1] Certain prior period amounts have been reclassified to conform to current period presentation. See Note 1 "Summary of Significant Accounting Policies" to the Consolidated Financial Statements for more information.