Investments (Tables)

3 Months Ended

Mar. 31, 2012

Investments [Abstract]

Available-For-Sale Investments

	As of:
	March 31, 2012							December 31, 2011							March 31, 2011
	Aggregate Fair Value		Amortized Cost		Net Unrealized Gains (Losses)			Aggregate Fair Value		Amortized Cost		Net Unrealized Gains (Losses)			Aggregate Fair Value		Amortized Cost		Net Unrealized Gains (Losses)
Available- for-Sale Investments:
Government obligations	$	80,445	$	80,446	($	1	)	$	100,517	$	100,480	$	37		$	100,658	$	100,691	($	33	)
Government agency obligations		17,022		17,022		0			31,351		31,354		(3	)		33,172		33,187		(15	)
Corporate obligations		17,339		17,340		(1	)		16,620		16,633		(13	)		13,437		13,441		(4	)
	$	114,806	$	114,808	($	2	)	$	148,488	$	148,467	$	21		$	147,267	$	147,319	($	52	)

Unrealized Gains And Losses On Available-For-Sale Investments

	Three Months Ended March 31,
	2012			2011
Unrealized gains	$	0		$	0
Unrealized losses	($	23	)	($	133	)

Components Of Investment Income

	Three Months Ended March 31,
	2012		2011
Interest income on investments	$	141	$	155
Realized net gains on the sale of investments		14		145
	$	155	$	300