Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($)
Changes in carrying amounts of goodwill
Balance at the beginning of the period	$ 432,888
Foreign currency translation	(297)
Balance at the end of the period	432,591
Region One
Changes in carrying amounts of goodwill
Balance at the beginning of the period	161,222
Foreign currency translation	(297)
Balance at the end of the period	160,925
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
Balance at the end of the period	62,664
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