Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended		0 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Apr. 30, 2014 ARS	Jun. 30, 2014 Fair value measured on a recurring basis Quoted prices in active markets (Level 1)	Dec. 31, 2013 Fair value measured on a recurring basis Quoted prices in active markets (Level 1)	Jun. 30, 2014 Fair value measured on a recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2013 Fair value measured on a recurring basis Significant other observable inputs (Level 2)	Jun. 30, 2014 Fair value measured on a recurring basis Significant unobservable inputs (Level 3)	Dec. 31, 2013 Fair value measured on a recurring basis Significant unobservable inputs (Level 3)	Jun. 30, 2014 Total Carrying Value	Mar. 31, 2014 Total Carrying Value	Dec. 31, 2013 Total Carrying Value
Assets:
Cash and cash equivalents				$ 139,858	$ 119,923					$ 139,858		$ 119,923
Restricted cash	42,627	42,594		42,627	42,594					42,627		42,594
Short-term investments						2,617	2,336			2,617		2,336
Investments in lieu of retainage				17,797	12,184	9,027	9,729			26,824		21,913
Long-term investments - auction rate securities									46,283		46,300	46,283
Total assets				200,282	174,701	11,644	12,065		46,283	211,926		233,049
Liabilities:
Interest rate swap contract						835	974			835		974
Contingent consideration								50,328	46,022	50,328		46,022
Total liabilities						835	974	50,328	46,022	51,163		46,996
Proceeds from sale of securities	$ 44,497		$ 44,500