Cash and Cash Equivalents (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash and Cash Equivalents [Abstract]
Cash deposits	$ 157,353				$ 131,271
Money market funds	102,380				160,790
Cash and cash equivalents	$ 259,733	$ 269,995	$ 263,052	$ 278,627	$ 292,061	$ 257,651	$ 215,448	$ 186,531	$ 159,856	$ 104,941