Summary of Significant Accounting Policies (Details 9) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Assets and liabilities carried at fair value measured on a recurring basis
Trading securities	$ 11,071	$ 9,124
Available-for-sale and Trading Securities
Number of trust that holds marketable securities	1
Net realized and unrealized gain (loss) on trading securities	1,292	(321)	1,221
Foreign Currency Cash Flow Hedges
Maximum Length of Time Hedged in Foreign Currency Cash Flow Hedge	P6M
Fair value measured on recurring basis | Total Carrying Value
Assets and liabilities carried at fair value measured on a recurring basis
Money market funds	68,800	35,110
Time deposits	149,829	146,713
Trading securities	11,071	9,124
Derivative assets		2,803
Derivative liabilities	1,522	435
Fair value measured on recurring basis | Quoted prices in active markets (Level 1)
Assets and liabilities carried at fair value measured on a recurring basis
Trading securities	10,525	8,497
Fair value measured on recurring basis | Significant other observable inputs (Level 2)
Assets and liabilities carried at fair value measured on a recurring basis
Money market funds	68,800	35,110
Time deposits	149,829	146,713
Trading securities	546	627
Derivative assets		2,803
Derivative liabilities	$ 1,522	$ 435