Stockholders' Equity (Stock Option Plan and Restricted Stock Activity) (Details)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Stock Options:
Balance as of December 31, 2016 (shares) | shares	1,754,275
Granted (shares) | shares	198,101
Exercised (shares) | shares	(80,872)
Forfeited (shares) | shares	0
Balance as of June 30, 2017 (shares) | shares	1,871,504
Weighted Average Exercise Price (in USD per share)
Balance as of December 31, 2016 | $ / shares	$ 42.12
Granted | $ / shares	101.93
Options exercised/RSUs vested | $ / shares	29.11
Forfeited | $ / shares	0.00
Balance as of June 30, 2017 | $ / shares	$ 49.02
Restricted Stock [Member]
Restricted Shares:
Nonvested at December 31, 2016 (shares) | shares	308,700
Granted (shares) | shares	68,151
Exercised (shares) | shares	(100,476)
Forfeited (shares) | shares	(300)
Nonvested at June 30, 2017 (shares) | shares	276,075
Weighted- Average Grant Date Fair Value (in USD per share)
Nonvested at December 31, 2016 | $ / shares	$ 86.61
Granted | $ / shares	101.64
Options exercised/RSUs vested | $ / shares	81.15
Forfeited | $ / shares	97.92
Nonvested at June 30, 2017 | $ / shares	$ 92.30