Fair Value Measurements (Measurement Inputs) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Liabilities:
Contingent purchase price	$ 188,554		$ 18,971
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Money market	46,019		14,751
U.S. government agency notes	0		0
Corporate debt securities	0		0
Total assets at fair value	46,019		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
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
U.S. government agency notes	0		0
Corporate debt securities	0		0
Total assets at fair value	0		0
Liabilities:
Contingent purchase price	188,554	100,524	18,971	22,633	21,568	20,431
Total liabilities at fair value	188,554		18,971
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Assets:
Money market	46,019		14,751
U.S. government agency notes	0		7,097
Corporate debt securities	0		43,778
Total assets at fair value	46,019		65,626
Liabilities:
Contingent purchase price	188,554		18,971
Total liabilities at fair value	$ 188,554		$ 18,971