Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($)
Changes in carrying amounts of goodwill
Balance at the beginning of the period	$ 432,888
Sale of business	(890)
Foreign currency translation	(541)
Balance at the end of the period	431,457
Region One
Changes in carrying amounts of goodwill
Balance at the beginning of the period	161,222
Foreign currency translation	(541)
Balance at the end of the period	160,681
Region Two
Changes in carrying amounts of goodwill
Balance at the beginning of the period	141,512
Balance at the end of the period	141,512
Region Three
Changes in carrying amounts of goodwill
Balance at the beginning of the period	36,389
Balance at the end of the period	36,389
Region Four
Changes in carrying amounts of goodwill
Balance at the beginning of the period	62,664
Sale of business	(890)
Balance at the end of the period	61,774
Region Five
Changes in carrying amounts of goodwill
Balance at the beginning of the period	31,101
Balance at the end of the period	$ 31,101