Stock-Based Compensation - Restricted Stock Activity (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Shares (in 000's)
Non-vested at beginning of period (in shares) | shares	153
Granted (in shares) | shares	132
Vested (in shares) | shares	(59)
Forfeited (in shares) | shares	(4)
Non-vested at end of period (in shares) | shares	222
Weighted-Average Grant Date Fair Value
Non-vested at beginning of period (in dollars per share) | $ / shares	$ 57.43
Granted (in dollars per share) | $ / shares	64.14
Vested (in dollars per share) | $ / shares	61.28
Forfeited (in dollars per share) | $ / shares	60.71
Non-vested at end of period (in dollars per share) | $ / shares	$ 60.34