Stock-Based Compensation, Nonvested Restricted Stock Awards (Details) - Restricted Stock Awards [Member]	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Number of Shares [Roll Forward]
Nonvested at beginning of year (in shares) | shares	467,500
Granted (in shares) | shares	341,900
Vested (in shares) | shares	(196,600)
Forfeited (in shares) | shares	(39,700)
Nonvested at end of year (in shares) | shares	573,100
Weighted-Average Grant Date Fair Value [Abstract]
Nonvested, beginning balance (in dollars per share) | $ / shares	$ 57.61
Granted (in dollars per share) | $ / shares	59.59
Vested (in dollars per share) | $ / shares	56.72
Forfeited (in dollars per share) | $ / shares	59.17
Nonvested, Ending Balance (in dollars per share) | $ / shares	$ 58.99