Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	$ 1,799,481	$ 1,595,368
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	873	1,743
Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	278,808	280,351
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	1,514,082	1,304,726
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	873	1,743
Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	6,591	10,291
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Cash and Cash Equivalents [Member] | Cash [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	268,171	227,528
Cash and Cash Equivalents [Member] | Cash [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	268,171	227,528
Cash and Cash Equivalents [Member] | Cash [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Cash [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	10,637	52,823
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	10,637	52,823
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Corporate Securities [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	594	389
Cash and Cash Equivalents [Member] | Corporate Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Corporate Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	594	389
Cash and Cash Equivalents [Member] | Corporate Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Available-for-sale Securities [Member] | Corporate Securities [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	744,630	644,091
Available-for-sale Securities [Member] | Corporate Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Corporate Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	738,039	633,800
Available-for-sale Securities [Member] | Corporate Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	6,591	10,291
Available-for-sale Securities [Member] | Agency Securities [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	623,927	454,750
Available-for-sale Securities [Member] | Agency Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Agency Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	623,927	454,750
Available-for-sale Securities [Member] | Agency Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Municipal Securities [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	31,251	53,756
Available-for-sale Securities [Member] | Municipal Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Municipal Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	31,251	53,756
Available-for-sale Securities [Member] | Municipal Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Government Securities [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	116,864	157,079
Available-for-sale Securities [Member] | Government Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Government Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	116,864	157,079
Available-for-sale Securities [Member] | Government Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Prepaid Expenses and Other Current Assets [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Foreign currency derivatives	3,407	4,952
Prepaid Expenses and Other Current Assets [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Prepaid Expenses and Other Current Assets [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Foreign currency derivatives	3,407	4,952
Prepaid Expenses and Other Current Assets [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Accrued Expenses and Other Current Liabilities [Member] | Estimate of Fair Value Measurement [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	873	1,743
Accrued Expenses and Other Current Liabilities [Member] | Level 1 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Accrued Expenses and Other Current Liabilities [Member] | Level 2 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	873	1,743
Accrued Expenses and Other Current Liabilities [Member] | Level 3 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	$ 0	$ 0