Segment Reporting - Reconciliation of Net Income to Adjusted Segment Earnings before Interest, Taxes, Depreciation and Amortization (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income	$ 62,645	$ 38,945
Add back:
Income tax provision	19,930	15,270
Interest income and other	(159)	1,800
Interest expense	4,746	6,244
Total Adjusted Segment EBITDA	117,490	95,281
Segment Reconciling Items
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income	62,645	38,945
Add back:
Income tax provision	19,930	15,270
Interest income and other	(159)	1,800
Interest expense	4,746	6,244
Unallocated corporate expenses	22,103	23,888
Segment depreciation expense	6,364	6,864
Amortization of intangible assets	1,861	2,270
Total Adjusted Segment EBITDA	$ 117,490	$ 95,281