Stockholder's Equity - Nonvested Stock Activity (Details)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Weighted average grant date fair value
Granted (in dollars per share)	$ 64.11
Restricted stock
Number of shares
Nonvested shares outstanding, beginning balance (in shares) | shares	529,465
Granted (in shares) | shares	257,175
Acquired (in shares) | shares	0
Vested (in shares) | shares	(211,355)
Nonvested shares outstanding, ending balance (in shares) | shares	575,285
Weighted average grant date fair value
Nonvested shares outstanding, beginning balance (in dollars per share)	$ 37.34
Granted (in dollars per share)	64.11
Acquired (in dollars per share)	0.00
Vested (in dollars per share)	37.78
Nonvested shares outstanding, ending balance (in dollars per share)	$ 49.66
Options
Number of shares
Nonvested shares outstanding, beginning balance (in shares) | shares	0
Granted (in shares) | shares	0
Acquired (in shares) | shares	270,710
Vested or exercised (in shares) | shares	(93,532)
Nonvested shares outstanding, ending balance (in shares) | shares	177,178
Weighted average grant date fair value
Nonvested shares outstanding, beginning balance (in dollars per share)	$ 0.00
Granted (in dollars per share)	0.00
Acquired (in dollars per share)	36.48
Vested or exercised (in dollars per share)	34.55
Nonvested shares outstanding, ending balance (in dollars per share)	$ 37.50