Short-term Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sale of Available-for-sale Securities	$ 239,370,000	$ 322,236,000	$ 60,000
Available-for-sale securities, amortized cost	130,971,000	90,648,000
Available-for-sale securities, gross unrealized gains	21,000	20,000
Available-for-sale securities, gross unrealized losses	(975,000)	(1,193,000)
Available-for-sale securities, fair value	130,017,000	89,475,000
Available-for-sale Securities, Gross Realized Gains	1,174,000	31,000
Available-for-sale Securities, Gross Realized Losses	981,000	555,000
Proceeds from Sale and Maturity of Marketable Securities		319,811,000	0
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	130,971,000	87,394,000
Available-for-sale securities, gross unrealized gains	21,000	20,000
Available-for-sale securities, gross unrealized losses	(975,000)	(411,000)
Available-for-sale securities, fair value	130,017,000	87,003,000
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost		3,254,000
Available-for-sale securities, gross unrealized gains		0
Available-for-sale securities, gross unrealized losses		(782,000)
Available-for-sale securities, fair value		$ 2,472,000
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Maturity Date	Dec. 31, 2014	Dec. 31, 2013
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Maturity Date	Dec. 31, 2015	Dec. 31, 2014