Share-Based Compensation (Details) $ / shares in Units, $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
Sep. 30, 2015USD ($)Rate$ / sharesshares | Sep. 30, 2014USD ($) | Sep. 30, 2015USD ($)Rate$ / sharesshares | Sep. 30, 2014USD ($) | Dec. 31, 2014$ / sharesshares |
Share-based compensation, allocation and classification in financial statements [Abstract] | | | | | |
Compensation cost charged to income for the Company's share-based compensation plans | $ | $ 1.3 | $ 3.9 | $ 8.9 | $ 11.2 | |
Reversal of Prior Period Share Based Compensation Expense | $ | 2.7 | | 2 | | |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount | $ | $ 0.2 | $ 0.4 | $ 1.6 | 1.5 | |
2008 Omnibus Plan [Member] | | | | | |
Deferred compensation arrangements [Abstract] | | | | | |
Aggregate number of Company common shares or Operating Partnership units approved for awards under the 2008 Omnibus Plan, amended (in shares) | 8,500,000 | | 8,500,000 | | |
The ratio at which non-option awards granted after the May 2010 amendment are deducted from the shares available for grant | Rate | 1.85 | | 1.85 | | |
The ratio at which non-option awards granted prior to the May 2010 amendment are deducted from the shares available for grant | Rate | 2.85 | | 2.85 | | |
The ratio at which options awards granted are deducted from the shares available for grant | | | one-for-one | | |
Employee Stock Option [Member] | | | | | |
Summary of option activity [Roll Forward] | | | | | |
Outstanding at January 1, 2015 | | | 521,293 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | | | (228,750) | | |
Outstanding at September 30, 2015 | 292,543 | | 292,543 | | 521,293 |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price | $ / shares | | | $ 29.72 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price | $ / shares | $ 46.60 | | $ 46.60 | | $ 39.20 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term | | | 1 year 7 months 28 days | | 1 year 7 months 6 days |
Fully vested options at September 30, 2015 | 292,543 | | 292,543 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price | $ / shares | $ 46.60 | | $ 46.60 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term | | | 1 year 7 months 28 days | | |
Summary of option activity, additional disclosures [Abstract] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | 0 | | |
Aggregate intrinsic value of in-the-money options outstanding | $ | $ 6.6 | | $ 6.6 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | $ | | | 10 | 1.4 | |
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options | $ | | | 6.8 | $ 1.8 | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options | $ | 0 | | $ 0 | | |
2014 Option Modification [Domain] | | | | | |
Summary of option activity [Roll Forward] | | | | | |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit | $ / shares | | | $ 35.50 | | $ 26.56 |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit | $ / shares | | | $ 51.15 | | $ 51.15 |
Unissued Partnership Units Under Unit Option Deferral Election Member | | | | | |
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract] | | | | | |
Options exercised under unit option deferral election plan (in shares) | | | 3,000,000 | | |
The number of mature units tendered for the exercise of previously issued stock options under the unit option deferral election plan (in shares) | | | 2,100,000 | | |
The number of units deferred under the unit option deferral election upon the exercise of previously issued stock options (in shares) | | | 900,000 | | |
Date at which deferred partnership units begin to be issued | | | December 2,017 | | |
Number of Annual Installments during which Deferred Partnership Units will be issued | | | ten | | |
Performance Shares [Member] | | | | | |
Summary of non-option activity, additional disclosures [Abstract] | | | | | |
Awards under the 2008 Omnibus Plan | | | Each PSU represents the right to receive, upon vesting, shares of the Company’s common stock ranging from 0-300% of the PSU based on the Company’s market performance relative to that of a peer group, plus a cash payment equal to the aggregate cash dividends that would have been paid on such shares of common stock from the date of grant of the award to the vesting date | | |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate | | | 1.12% | | |
Share-based Compensation Arrangement by Share-based Payment Award, Vesting Period | | | 3 years | | |
Weighted average grant-date fair value | $ / shares | | | $ 112.30 | | |
Right to Receive Upon Vesting Shares of Common Stock as Percentage of PSU, Actual Vested During Period | | | 0 | | |
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized | $ | $ 10.5 | | $ 10.5 | | |
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition | | | 1 year 8 months 1 day | | |
Summary of non-option activity [Roll Forward] | | | | | |
Outstanding at January 1, 2015 | | | 254,651 | | |
Vested | | | (43,575) | | |
Granted | | | 50,256 | | |
Forfeited | | | (5,854) | | |
Outstanding at September 30, 2015 | 255,478 | | 255,478 | | 254,651 |
Outstanding at beginning of period, weighted average grant date fair value (in dollars per share) | $ / shares | | | $ 132.86 | | |
Vested, weighted average grant date fair value (in dollars per share) | $ / shares | | | 97.44 | | |
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | | | 112.30 | | |
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares | | | 174.95 | | |
Outstanding at end of period, weighted average grant date fair value (in dollars per share) | $ / shares | $ 134.52 | | $ 134.52 | | $ 132.86 |
Restricted Stock Units (RSUs) [Member] | | | | | |
Summary of non-option activity, additional disclosures [Abstract] | | | | | |
Awards under the 2008 Omnibus Plan | | | represent the right to receive upon vesting one share of the Company’s common stock, plus a cash payment equal to the aggregate cash dividends that would have been paid on such shares of common stock from the date of grant of the award to the vesting date | | |
Weighted average grant-date fair value | $ / shares | | | $ 74.36 | | |
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized | $ | $ 7.9 | | $ 7.9 | | |
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition | | | 1 year 10 months 13 days | | |
Summary of non-option activity [Roll Forward] | | | | | |
Outstanding at January 1, 2015 | | | 293,651 | | |
Vested | | | (94,835) | | |
Granted | | | 100,682 | | |
Forfeited | | | (13,884) | | |
Outstanding at September 30, 2015 | 285,614 | | 285,614 | | 293,651 |
Outstanding at beginning of period, weighted average grant date fair value (in dollars per share) | $ / shares | | | $ 67 | | |
Vested, weighted average grant date fair value (in dollars per share) | $ / shares | | | 65.56 | | |
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | | | 74.36 | | |
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares | | | 69.90 | | |
Outstanding at end of period, weighted average grant date fair value (in dollars per share) | $ / shares | $ 69.92 | | $ 69.92 | | $ 67 |