Share-Based Transactions - Nonemployee Share-Based Transactions, Cost and Tax Benefit (Details) (Nonemployee Shares [Member], USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Goods And Nonemployee Services Transaction [Line Items]
Total quarterly non-employee RSUs granted		294,985
Measurement date per-share fair value of awards	$42.96 to $49.98	$42.96 to $49.98	$26.39 to $36.44
Illiquidity discounts	8% to 9%	8% to 9%	13% to 18%
Expense Recognized [Member]
Share Based Goods And Nonemployee Services Transaction [Line Items]
Quarterly incentive awards expense		453
Expense Deferred [Member]
Share Based Goods And Nonemployee Services Transaction [Line Items]
Quarterly incentive awards expense		13,598
Tax Benefit of Deferred Expense [Member]
Share Based Goods And Nonemployee Services Transaction [Line Items]
Quarterly incentive awards expense		4,500