Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of Cash Flows [Abstract]
Cash paid for operating lease liabilities	$ 69,317
Income tax refund received	2,216	$ 8,656
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	515,896	977,488
Restricted cash	373	851
Cash, cash equivalents and restricted cash	516,269	$ 978,339
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	$ 63,709