Share-Based Compensation - Employee Stock Purchase Plan (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) offering shares	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	1,300
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Continuous years of service	2 years
Number of additional offerings | offering	5
Stock options authorized to issue to employees (in shares)	4,100
Shares available for future grant (in shares)	2,300
Common shares purchased (in shares)	53	59	55
Annual earnings withheld to purchase common stock | $	$ 21,250
Percent of IRS limitation	85.00%
Maximum fair value of common stock purchased | $	$ 25,000