Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liabilities:
Contingent purchase price	$ 302,363	$ 18,971
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Money market		14,751
US treasury notes	0	0
U.S. government agency notes	0	0
Corporate debt securities	0	0
Total assets at fair value	0	14,751
Liabilities:
Contingent purchase price	0	0
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Money market	0	0
US treasury notes	0	0
U.S. government agency notes	0	7,097
Corporate debt securities	0	43,778
Total assets at fair value	0	50,875
Liabilities:
Contingent purchase price	0	0
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Money market	0	0
US treasury notes	0	0
U.S. government agency notes	0	0
Corporate debt securities	0	0
Total assets at fair value	0	0
Liabilities:
Contingent purchase price	302,363	18,971	20,431
Total liabilities at fair value	302,363	18,971
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Assets:
Money market	0	14,751
US treasury notes	0	0
U.S. government agency notes	0	7,097
Corporate debt securities	0	43,778
Total assets at fair value	0	65,626
Liabilities:
Contingent purchase price	302,363	18,971
Total liabilities at fair value	$ 302,363	$ 18,971