Stock-Based Compensation	6 Months Ended
Stock-Based Compensation	Jun. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	11. Stock-Based Compensation During the quarter ended March 31, 2016, the Corporation awarded its annual grant of stock-based compensation, which included 75,421 of performance stock units and 68,720 of restricted stock units. The grant-date fair value of each award is $142.02 for the performance stock units and $124.41 for the restricted stock units. No stock options are expected to be awarded in 2016. In past years, annual stock-based compensation awards were primarily made in the second quarter of the year. The change in the composition of the awards and the timing of the annual grant resulted in higher expense recorded in the first half of the year compared with prior years. For the six months ended June 30, 2016 and 2015, stock-based compensation expense was $12,801,000 and $7,524,000, respectively.

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.