Business Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reconciliation of segment profit to income before income taxes
Segment profit	$ 44,995	$ 75,048	$ 121,544	$ 144,281
Stock compensation expense	(9,550)	(4,602)	(14,022)	(10,240)
Non-controlling interest segment profit (loss)	(648)		(1,978)
Depreciation and amortization	(22,480)	(16,946)	(42,709)	(33,116)
Interest expense	(2,004)	(792)	(2,840)	(1,402)
Interest income	275	358	586	711
Income before income taxes	$ 10,588	$ 53,066	$ 60,581	$ 100,234