Stock-based Compensation Expense Activity in Performance Unit Awards (Details) - Performance Unit Awards	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Shares
Nonvested, beginning of period (in shares) | shares	456,018
Granted (in shares) | shares	214,610
Vested (in shares) | shares	(43,177)
Forfeited (in shares) | shares	(130,246)
Nonvested, end of period (in shares) | shares	497,205
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (in dollars per share) | $ / shares	$ 66.21
Granted (in dollars per share) | $ / shares	55.34
Vested (in dollars per share) | $ / shares	65.39
Forfeited (in dollars per share) | $ / shares	64.50
Nonvested, end of period (in dollars per share) | $ / shares	$ 62.04