Equity Compensation (Details 2) - Employee Stock Purchase Plan - $ / shares	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Employee Stock Purchase Plan.
Common stock purchase price to eligible employees (as a percent)	90.00%
Percentage of Black Scholes Methodology Used for Valuation of Lookback Feature	90.00%
Percentage of maximum subscription price used as a component to calculate value of lookback feature	10.00%
Shares available for issuance	764,645
Subscriptions outstanding (in shares)	59,529	58,627
Maximum subscription price (in dollars per share)	$ 21.43	$ 21.43
Shares of stock issued	56,193	56,942
Stock issuance price (in dollars per share)	$ 21.01	$ 19.58
Assumptions for valuation of shares
Fair value of grants (in dollars per share)	$ 3.58	$ 3.07
Risk-free interest rate (as a percent)	0.26%	0.10%
Dividend yield (as a percent)	4.40%	4.30%
Expected volatility (as a percent)	21.00%	14.00%
Expected life in months	12 months	12 months