Consolidated Statement of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in-Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	3.00% Notes [Member]	3.00% Notes [Member] Additional Paid-in-Capital	2.25% Convertible Notes [Member]	2.25% Convertible Notes [Member] Additional Paid-in-Capital	2.25% Convertible Notes [Member] Treasury Stock
Beginning balance at Dec. 31, 2012	$ 860,284	$ 258	$ 332,836	$ 677,864	$ (33,057)	$ (117,617)
Beginning balance, shares at Dec. 31, 2012		25,836
Net income	113,992
Other comprehensive income (loss), net	(18,620)				(18,620)
Equity component of 3.00% Convertible Note issuance, net of deferred tax liability	3,411		3,411
Stock Issued During Period, Shares, Employee Stock Purchase Plans		(90)
Stock Issued During Period, Value, Employee Stock Purchase Plan	1,823	$ 1	12,137	0	0	10,315
Purchases of treasury stock	(3,554)					(3,554)
Treasury stock used in acquisition	80,398		27,689			52,709
Stock-based compensation	16,842		16,842
Cash dividends	(15,755)			(15,755)
Ending balance at Dec. 31, 2013	1,035,175	$ 257	368,641	776,101	(51,677)	(58,147)
Ending balance, shares at Dec. 31, 2013		25,746
Net income	93,004
Other comprehensive income (loss), net	(30,307)				(30,307)
Equity component of 3.00% Convertible Note issuance, net of deferred tax liability	(14,163)		(14,163)
Stock Issued During Period, Shares, Employee Stock Purchase Plans		(22)
Stock Issued During Period, Value, Employee Stock Purchase Plan	321	$ 0	13,008	0	0	12,687
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments							$ (118,044)	$ (118,044)	$ (16,071)	$ 20,789
Stock Issued During Period, Value, Conversion of Convertible Securities											$ 36,860
Call Options and Warrant Equity Settlement	32,641							$ 32,641	$ 0	$ 33,772	$ (33,772)
Purchases of treasury stock	(36,802)					(36,802)
Stock-based compensation	17,804		17,804
Cash dividends	(17,048)			(17,048)
Ending balance at Dec. 31, 2014	978,010	$ 257	286,854	852,057	(81,984)	(79,174)
Ending balance, shares at Dec. 31, 2014		25,724
Net income	93,999
Other comprehensive income (loss), net	(56,000)				(56,000)
Stock Issued During Period, Shares, Employee Stock Purchase Plans		(18)
Stock Issued During Period, Value, Employee Stock Purchase Plan	(206)		16,701	0	0	16,907
Purchases of treasury stock	(99,015)					(99,015)
Stock-based compensation	20,939		20,939
Cash dividends	(19,887)			(19,887)
Ending balance at Dec. 31, 2015	$ 918,252	$ 257	$ 291,092	$ 926,169	$ (137,984)	$ (161,282)
Ending balance, shares at Dec. 31, 2015		25,706