Cash, Cash Equivalents and Short-term Investments Classification by contractual maturity of cash, cash equivalents and short-term investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 39,652	$ 92,521
Available-for-sale Securities	88,024	34,989
Cash, Cash Equivalents And Short Term Investments, Fair Value Disclosure	127,676	127,510
Maturity up to one year [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	39,652	92,521
Available-for-sale Securities	71,464	34,989
Cash, Cash Equivalents And Short Term Investments, Fair Value Disclosure	111,116	127,510
maturity between 1 and 2 years [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Available-for-sale Securities	16,560	0
Cash, Cash Equivalents And Short Term Investments, Fair Value Disclosure	$ 16,560	$ 0