CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other comprehensive (loss)/income:
Unrealized gains on investment, tax expense	$ 15	$ 112	$ 305
Reclassification of realized gains on sales of investments to earnings, tax expense	(95)	(309)
Unrealized gains/losses on swap derivatives to earnings, tax expense			105
Reclassifications of net losses on swap derivatives to earnings, tax benefit		(349)
Other-than-temporary loss on investments, tax benefit			$ 765