Stock-Based Compensation (Details 1) shares in Thousands	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of options (in thousands)
Options outstanding at beginning of period (in shares) | shares	2,887
Options granted (in shares) | shares	1,034
Options exercised (in shares) | shares	(833)
Options forfeited (in shares) | shares	(24)
Options expired (in shares) | shares	0
Options outstanding at end of period (in shares) | shares	3,064
Weighted average exercise price
Weighted average exercise price, Options outstanding Beginning Balance (usd per share) | $ / shares	$ 15.59
Weighted average exercise price, Options granted (usd per share) | $ / shares	27.09
Weighted average exercise price, Options exercised (usd per share) | $ / shares	9.20
Weighted average exercise price, Options forfeited (usd per share) | $ / shares	23.81
Weighted average exercise price, Options expired (usd per share) | $ / shares	0.00
Weighted average exercise price, Options outstanding Ending Balance (usd per share) | $ / shares	$ 21.14