Stock-Based Compensation and Other Employee Benefit Plans (Schedule of Non-Cash Stock-Based Compensation Expense) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-Based Compensation and Other Employee Benefit Plans [Line Items]
Non-cash stock-based compensation expense			$ 15,656	$ 15,072	$ 12,395
Income Tax Effects:
Income tax effect of non-cash stock-based compensation			11,200	5,600	4,200
Excess tax benefit from non-cash stock-based compensation	[1]		5,700	100	100
Tax benefit, net			(22,942)	(91,784)	(11,957)
Share-Based Compensation [Member]
Income Tax Effects:
Tax benefit, net		$ 5,600	5,400
General and Administrative Expenses [Member]
Stock-Based Compensation and Other Employee Benefit Plans [Line Items]
Non-cash stock-based compensation expense			$ 15,700	$ 15,100	$ 12,400

[1] Excess tax benefits represent cash flows from tax deductions in excess of the tax effect of compensation expense associated with share-based payment arrangements. For the year ended December 31, 2017, the Company recognized a tax benefit of $5.4 million, net of tax deficiencies, related to the vesting of share-based payment awards.