Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Total assets	$ 1,528,101	$ 1,480,432
Total liabilities	4,162	8,454
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Total assets	627,133	291,123
Total liabilities
Significant Other Observable Inputs (Level 2) [Member]
Total assets	897,627	1,185,613
Total liabilities	4,162	8,454
Significant Unobservable Inputs (Level 3) [Member]
Total assets	3,341	3,696
Total liabilities
Foreign currency derivatives
Foreign currency derivatives	4,157	2,831
Foreign currency derivatives \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Foreign currency derivatives
Foreign currency derivatives \| Significant Other Observable Inputs (Level 2) [Member]
Foreign currency derivatives	4,157	2,831
Foreign currency derivatives \| Significant Unobservable Inputs (Level 3) [Member]
Foreign currency derivatives
Foreign currency derivatives
Foreign currency derivatives	4,162	8,454
Foreign currency derivatives \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Foreign currency derivatives
Foreign currency derivatives \| Significant Other Observable Inputs (Level 2) [Member]
Foreign currency derivatives	4,162	8,454
Foreign currency derivatives \| Significant Unobservable Inputs (Level 3) [Member]
Foreign currency derivatives
Money market funds \| Cash and Cash Equivalents [Member]
Fair value of cash and cash equivalents	123,519	101,056
Money market funds \| Cash and Cash Equivalents [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of cash and cash equivalents	123,519	101,056
Money market funds \| Cash and Cash Equivalents [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of cash and cash equivalents	0	0
Money market funds \| Cash and Cash Equivalents [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of cash and cash equivalents	0	0
Corporate securities \| Cash and Cash Equivalents [Member]
Fair value of cash and cash equivalents	16,476	38,738
Corporate securities \| Cash and Cash Equivalents [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of cash and cash equivalents	0	0
Corporate securities \| Cash and Cash Equivalents [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of cash and cash equivalents	16,476	38,738
Corporate securities \| Cash and Cash Equivalents [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of cash and cash equivalents	0	0
Cash \| Cash and Cash Equivalents [Member]
Fair value of cash and cash equivalents	503,614	190,067
Cash \| Cash and Cash Equivalents [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of cash and cash equivalents	503,614	190,067
Cash \| Cash and Cash Equivalents [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of cash and cash equivalents	0	0
Cash \| Cash and Cash Equivalents [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of cash and cash equivalents	0	0
Agency securities \| Available-For-Sale Securities [Member]
Fair value of investments	402,707	646,224
Agency securities \| Available-For-Sale Securities [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of investments
Agency securities \| Available-For-Sale Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of investments	402,707	646,224
Agency securities \| Available-For-Sale Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of investments
Corporate securities \| Available-For-Sale Securities [Member]
Fair value of investments	405,322	391,793
Corporate securities \| Available-For-Sale Securities [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of investments
Corporate securities \| Available-For-Sale Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of investments	401,981	388,097
Corporate securities \| Available-For-Sale Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of investments	3,341	3,696
Municipal securities \| Cash and Cash Equivalents [Member]
Fair value of cash and cash equivalents		3,435
Municipal securities \| Cash and Cash Equivalents [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of cash and cash equivalents		0
Municipal securities \| Cash and Cash Equivalents [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of cash and cash equivalents		3,435
Municipal securities \| Cash and Cash Equivalents [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of cash and cash equivalents		0
Municipal securities \| Available-For-Sale Securities [Member]
Fair value of investments	32,313	80,026
Municipal securities \| Available-For-Sale Securities [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of investments
Municipal securities \| Available-For-Sale Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of investments	32,313	80,026
Municipal securities \| Available-For-Sale Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of investments
Government securities \| Available-For-Sale Securities [Member]
Fair value of investments	39,993	26,262
Government securities \| Available-For-Sale Securities [Member] \| Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair value of investments
Government securities \| Available-For-Sale Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair value of investments	39,993	26,262
Government securities \| Available-For-Sale Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of investments

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

+ References+ Details