Shareholders' Equity and Common Stock Equivalents - Restricted Stock Activity (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Total Outstanding Units
Beginning balance, Total Outstanding, Units (in shares) | shares	1,419,268
Granted, Total Outstanding Units (in shares) | shares	193,044
Vested, Total Outstanding Units (in shares) | shares	0
Forfeited, Total Outstanding Units (in shares) | shares	(72,953)
Distributed, Total Outstanding Units (in shares) | shares	(389,680)
Ending balance, Total Outstanding, Units (in shares) | shares	1,149,679
Total Outstanding Units, Weighted Average Grant Date Fair Value per Unit
Beginning balance, Total Outstanding, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	$ 27.63
Granted, Total Outstanding, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	40.77
Vested, Total Outstanding, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	0
Forfeited, Total Outstanding, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	32.58
Distributed, Total Outstanding, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	20.16
Ending balance, Total Outstanding, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	$ 32.05
Vested Units
Beginning balance, Vested, Units (in shares) | shares	768,064
Granted, Vested, Units (in shares) | shares	0
Vested, Vested, Units (in shares) | shares	179,755
Forfeited, Vested, Units (in shares) | shares	0
Distributed, Vested, Units (in shares) | shares	(389,680)
Ending balance, Vested, Units (in shares) | shares	558,139
Vested Units, Weighted Average Grant Date Fair Value per Unit
Beginning balance, Vested, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	$ 16.80
Granted, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	0
Vested, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	29.15
Forfeited, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	0
Distributed, Vested, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	20.16
Ending balance, Vested, Weighted Average Grant Date Fair Value per Unit (in usd per share) | $ / shares	$ 19.80