Stock-based Compensation Expense Activity in Performance Unit Awards (Details) - Performance Unit Awards	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Shares
Nonvested, beginning of period (in shares) | shares	497,205
Granted (in shares) | shares	139,948
Vested (in shares) | shares	(80,970)
Forfeited (in shares) | shares	(61,492)
Nonvested, end of period (in shares) | shares	494,691
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (in dollars per share) | $ / shares	$ 62.04
Granted (in dollars per share) | $ / shares	78.03
Vested (in dollars per share) | $ / shares	61.75
Forfeited (in dollars per share) | $ / shares	63.61
Nonvested, end of period (in dollars per share) | $ / shares	$ 66.42