10. Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets:
Marketable securities	$ 492,875	$ 439,102
Foreign Agency Debt [Member]
Assets:
Marketable securities	452,565	364,046
Bank Time Deposits [Member]
Assets:
Marketable securities	30,000	0
Federal Agency Debt [Member]
Assets:
Marketable securities	6,807	46,439
US Government Debt Securities [Member]
Assets:
Marketable securities	3,503	3,502
Foreign Government Obligations [Member]
Assets:
Marketable securities	0	25,115
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Assets:
Restricted investments (excluding restricted cash)	330,196	279,274
Derivative assets	6,354	8,278
Total assets	838,181	729,543
Liabilities:
Derivative liabilities	9,417	16,204
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Foreign Agency Debt [Member]
Assets:
Marketable securities	452,565	364,046
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Bank Time Deposits [Member]
Assets:
Marketable securities	30,000
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Federal Agency Debt [Member]
Assets:
Marketable securities	6,807	46,439
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | US Government Debt Securities [Member]
Assets:
Marketable securities	3,503	3,502
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Foreign Government Obligations [Member]
Assets:
Marketable securities		25,115
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	8,756	2,889
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Restricted investments (excluding restricted cash)	0	0
Derivative assets	0	0
Total assets	38,756	2,889
Liabilities:
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Agency Debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Bank Time Deposits [Member]
Assets:
Marketable securities	30,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Federal Agency Debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Obligations [Member]
Assets:
Marketable securities		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	8,756	2,889
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Restricted investments (excluding restricted cash)	330,196	279,274
Derivative assets	6,354	8,278
Total assets	799,425	726,654
Liabilities:
Derivative liabilities	9,417	16,204
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Agency Debt [Member]
Assets:
Marketable securities	452,565	364,046
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Bank Time Deposits [Member]
Assets:
Marketable securities	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Federal Agency Debt [Member]
Assets:
Marketable securities	6,807	46,439
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Assets:
Marketable securities	3,503	3,502
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Obligations [Member]
Assets:
Marketable securities		25,115
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Restricted investments (excluding restricted cash)	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Agency Debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Bank Time Deposits [Member]
Assets:
Marketable securities	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Federal Agency Debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Obligations [Member]
Assets:
Marketable securities		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	$ 0	$ 0