Marketable Securities - Maturities of Held to Maturity Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Marketable Securities [Abstract]
Due within one year	$ 25,504
Due in one to five years	76,563
Total	$ 102,067us-gaap_HeldToMaturitySecurities

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Name:	us-gaap_HeldToMaturitySecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant