Fair Value of Assets and Liabilities - Securities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
U.S. treasury notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	$ 10,128		$ 60,786
Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	37,961	[1]	31,157	[1]
Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	39,987		5,000
Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	7,786		5,494
Municipal bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	49,319		3,228
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	5,001
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	5,287		3,046
Derivative contracts, net	(1,113)		1,655
Assets, fair value	154,356		110,366
Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. treasury notes [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	10,128		60,786
Estimate of Fair Value, Fair Value Disclosure [Member] | Agency bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	37,961		31,157
Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	39,987		5,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	7,786		5,494
Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	49,319		3,228
Estimate of Fair Value, Fair Value Disclosure [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	5,001
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	5,287		3,046
Derivative contracts, net	0		0
Assets, fair value	15,415		63,832
Fair Value, Inputs, Level 1 [Member] | U.S. treasury notes [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	10,128		60,786
Fair Value, Inputs, Level 1 [Member] | Agency bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 1 [Member] | Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 1 [Member] | Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 1 [Member] | Municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	0		0
Derivative contracts, net	(1,113)		1,655
Assets, fair value	138,941		46,534
Fair Value, Inputs, Level 2 [Member] | U.S. treasury notes [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 2 [Member] | Agency bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	37,961		31,157
Fair Value, Inputs, Level 2 [Member] | Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	39,987		5,000
Fair Value, Inputs, Level 2 [Member] | Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	7,786		5,494
Fair Value, Inputs, Level 2 [Member] | Municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	49,319		3,228
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	5,001
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	0		0
Derivative contracts, net	0		0
Assets, fair value	0		0
Fair Value, Inputs, Level 3 [Member] | U.S. treasury notes [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 3 [Member] | Agency bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 3 [Member] | Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 3 [Member] | Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0		0
Fair Value, Inputs, Level 3 [Member] | Municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	$ 0		$ 0

[1] Agency bonds are securities backed by U.S. government-sponsored entities.