Available-for-Sale Securities and Fair Value Measurements (Details 2) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	$ 316,743,000	$ 502,831,000
U.S. government securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	33,564,000	42,158,000
U.S. government agency securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	43,614,000	141,331,000
U.S. corporate notes
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	59,607,000	94,977,000
U.S. commercial paper
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	44,434,000	102,022,000
Equity securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	10,068,000
Money market funds
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	125,456,000	122,343,000
Recurring basis | U.S. government securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	33,564,000	42,158,000
Recurring basis | U.S. government agency securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	43,614,000	141,331,000
Recurring basis | U.S. corporate notes
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	59,607,000	94,977,000
Recurring basis | U.S. commercial paper
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	44,434,000	102,022,000
Recurring basis | Equity securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	10,068,000
Recurring basis | Money market funds
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	125,456,000	122,343,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets, Level 1
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	169,088,000	327,827,000
Fair value measured transfer to Level 2 From Level 1		5,400,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets, Level 1 | U.S. government securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	33,564,000	42,158,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets, Level 1 | U.S. government agency securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	0	98,236,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets, Level 1 | U.S. corporate notes
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	0	61,591,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets, Level 1 | U.S. commercial paper
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	0	3,499,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets, Level 1 | Equity securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	10,068,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets, Level 1 | Money market funds
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	125,456,000	122,343,000
Recurring basis | Significant Other Observable Inputs, Level 2
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	147,655,000	175,004,000
Fair value measured transfer to Level 2 From Level 1	5,400,000
Recurring basis | Significant Other Observable Inputs, Level 2 | U.S. government agency securities
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	43,614,000	43,095,000
Recurring basis | Significant Other Observable Inputs, Level 2 | U.S. corporate notes
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	59,607,000	33,386,000
Recurring basis | Significant Other Observable Inputs, Level 2 | U.S. commercial paper
Estimated fair values of entity's financial assets and liabilities
Total assets measured at fair value	44,434,000	98,523,000
Nonrecurring basis
Estimated fair values of entity's financial assets and liabilities
Convertible subordinated notes due 2023	239,339,000	408,250,000
Non-recourse notes due 2029	454,500,000
Total fair value of liabilities	693,839,000
Nonrecurring basis | Significant Other Observable Inputs, Level 2
Estimated fair values of entity's financial assets and liabilities
Convertible subordinated notes due 2023	239,339,000	408,250,000
Non-recourse notes due 2029	454,500,000
Total fair value of liabilities	$ 693,839,000