Stockholders' Equity (Stock Option Plan and Restricted Stock Activity) (Details)	3 Months Ended
	Mar. 31, 2017 $ / shares shares
Stock Options:
Balance as of December 31, 2016 (shares) | shares	1,754,275
Granted (shares) | shares	180,765
Exercised (shares) | shares	(29,412)
Forfeited (shares) | shares	0
Balance as of March 31, 2017 (shares) | shares	1,905,628
Weighted Average Exercise Price (in USD per share)
Balance as of December 31, 2016 | $ / shares	$ 42.12
Granted | $ / shares	100.81
Exercised | $ / shares	17.42
Forfeited | $ / shares	0.00
Balance as of March 31, 2017 | $ / shares	$ 48.07
Restricted Stock [Member]
Restricted Shares:
Nonvested at December 31, 2015 (shares) | shares	308,700
Granted (shares) | shares	64,155
Exercised (shares) | shares	(96,744)
Forfeited (shares) | shares	(300)
Nonvested at June 30, 2016 (shares) | shares	275,811
Weighted- Average Grant Date Fair Value (in USD per share)
Nonvested at December 31, 2015 | $ / shares	$ 86.61
Granted | $ / shares	100.91
Exercised | $ / shares	79.68
Forfeited | $ / shares	97.92
Nonvested at March 31, 2016 | $ / shares	$ 92.36