Goodwill (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Changes in carrying amounts of goodwill
Balance at the beginning of the period	$ 435,122
Adjustment to purchase price allocation	(966)
Foreign currency translation	(279)
Balance at the end of the period	433,877
Region One
Changes in carrying amounts of goodwill
Balance at the beginning of the period	191,941
Adjustment to purchase price allocation	(312)
Balance at the end of the period	191,629
Region Two
Changes in carrying amounts of goodwill
Balance at the beginning of the period	31,840
Adjustment to purchase price allocation	(103)
Balance at the end of the period	31,737
Region Three
Changes in carrying amounts of goodwill
Balance at the beginning of the period	65,770
Adjustment to purchase price allocation	(111)
Foreign currency translation	(279)
Balance at the end of the period	65,380
Region Four
Changes in carrying amounts of goodwill
Balance at the beginning of the period	62,052
Adjustment to purchase price allocation	(145)
Balance at the end of the period	61,907
Region Five
Changes in carrying amounts of goodwill
Balance at the beginning of the period	83,519
Adjustment to purchase price allocation	(295)
Balance at the end of the period	$ 83,224