Stock Option Valuation Assumptions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected volatility	0.00%	[1]	40.20%	[1]	43.80%	[1]
Expected term of share-based compensation awards	0 years	[2]
Expected term (years)			6 years 11 months	[2]	6 years 9 months	[2]
Risk free interest rate	0.00%	[3]	1.30%	[3]	1.30%	[3]
Expected dividend yield	0.00%	[4]	2.40%	[4]	2.10%	[4]
Annualized dividend per share used in calculation of expected dividend yield	$ 0.38		$ 0.30		$ 0.24

[1] The expected volatility used to estimate the fair value of stock options awarded is based on a blend of: (i) historical volatility of our common stock for periods equal to the expected term of our stock options and (ii) implied volatility of tradable forward put and call options to purchase and sell shares of our common stock.

[2] The estimate of our expected term is based on the average of (i) an assumption that all outstanding options are exercised upon achieving their full vesting date and (ii) an assumption that all outstanding options will be exercised at the midpoint between the current date (i.e., the date awards have ratably vested through) and their full contractual term. In determining the estimate, we considered several factors, including the historical option exercise behavior of our employees and the terms and vesting periods of the options.

[3] The risk free rate is determined using the implied yield currently available for zero-coupon U.S. government issuers with a remaining term equal to the expected term of the options.

[4] The expected dividend yield is calculated based on an annualized dividend of $0.38 per share in 2014, $0.30 per share in 2013 and $0.24 per share in 2012.