Stock-Based Compensation - Restricted Stock Activity (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Shares (in 000's)
Non-vested at beginning of period (in shares) | shares	153
Granted (in shares) | shares	99
Vested (in shares) | shares	(43)
Forfeited (in shares) | shares	(4)
Non-vested at end of period (in shares) | shares	205
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	63.40
Vested (in dollars per share) | $ / shares	59.64
Forfeited (in dollars per share) | $ / shares	60.64
Non-vested at end of period (in dollars per share) | $ / shares	$ 59.78