Long-term Debt - Credit Facility (Details) (USD $)										12 Months Ended			12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011 Senior Secured Credit Facility [Member]	Aug. 02, 2011 Senior Secured Credit Facility [Member]	Dec. 31, 2011 Letter of Credit [Member]	Aug. 02, 2011 Letter of Credit [Member]	Dec. 31, 2011 ACDL [Member]	Dec. 31, 2011 Minimum [Member] Senior Secured Credit Facility [Member]	Dec. 31, 2011 Minimum [Member] Senior Secured Credit Facility [Member] LIBOR [Member]	Dec. 31, 2011 Minimum [Member] Senior Secured Credit Facility [Member] Base Rate [Member]	Dec. 31, 2011 Maximum [Member] Senior Secured Credit Facility [Member]	Dec. 31, 2011 Maximum [Member] Senior Secured Credit Facility [Member] LIBOR [Member]	Dec. 31, 2011 Maximum [Member] Senior Secured Credit Facility [Member] Base Rate [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 410,000,000		$ 375,000,000
Line of credit facility, amount outstanding							11,100,000
Basis spread on variable rate											1.75%	0.25%		3.50%	2.00%
Commitment fee percentage										0.25%			0.75%
Maximum consolidated total leverage					7.25
Minimum consolidated interest coverage ratio					1.50
Maximum consolidated senior secured debt ratio					2.75
Covenant limit					1,500,000,000
Ratio of indebtedness to net capital, minimum					6.0
Maximum outstanding equity interests of foreign restricted subsidiaries					66.00%
Cash and cash equivalents	$ 80,294,000	$ 195,387,000	$ 129,576,000	$ 115,712,000					$ 15,000,000