Summary of Significant Accounting Policies (Details Textual) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Summary of Significant Accounting Policies (Textual) [Abstract]
Restricted cash	$ 4,100,000
Proceeds from sale/maturity of short-term investments	$ 29,500,000	$ 12,100,000
Short-term investment contractual maturities	1 year		1 year
Cash equivalents, maturity period	Three months or less

The cash inflow from sales, maturities, prepayments, calls and collections of all investments, including securities and other assets, having ready marketability and intended by management to be liquidated, if necessary, within the current operating cycle. Includes cash flows from securities classified as trading securities that were acquired for reasons other than sale in the short-term.

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The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

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