Acquisitions (Schedule of Supplemental Pro Forma Consolidated Results of Operations) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues	$ 184,087	$ 99,270	$ 366,436	$ 198,066
Net income	69,579	35,401	98,616	36,904
Earnings Per Share, Basic	$ 1.77	$ 0.90	$ 2.51	$ 0.94
Earnings Per Share, Diluted	$ 1.75	$ 0.90	$ 2.48	$ 0.94
Pro Forma Revenue		144,076		300,702
Pro Forma Net income		40,043		42,306
Pro Forma Basic earnings per share		$ 1.03		$ 1.08
Pro Forma Diluted earnings per share		$ 1.03		$ 1.07
Parent Company [Member]
Revenues	164,706	74,059	323,995	147,086
Net income	$ 69,579	$ 35,401	$ 98,616	$ 36,904