Common Stock (Stock Option Activity and Additional Details) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0	0	0
Shares (in shares)
Outstanding, beginning of period (in shares)	777,400
Exercised (in shares)	(114,112)	(767,560)
Forfeited (in shares)	0
Expired (in shares)	0
Outstanding, end of period (in shares)	663,288	777,400
Vested or expected to vest (in shares)	663,288
Options exercisable (in shares)	663,288
Weighted-Average Exercise Price (in dollars per share)
Outstanding, beginning of period (in dollars per share)	$ 7.80
Exercised (in dollars per share)	1.62
Forfeited (in dollars per share)	0.00
Expired (in dollars per share)	0.00
Outstanding, end of period (in dollars per share)	8.87	$ 7.80
Vested or expected to vest (in dollars per share)	8.87
Options exercisable (in dollars per share)	$ 8.87
Weighted Average Remaining Conctracual Term (in years)
Outstanding	5 months 1 day
Vesting or expected to vest	5 months 1 day
Options exercisable	5 months 1 day
Aggregate Intrinsic Value
Outstanding	$ 348,067
Vesting or expected to vest	348,067
Options exercisable	348,067
Stock Options, Additional Disclosures
Total intrinsic value of stock options exercised	$ 1,000,000	$ 8,400,000	$ 6,000,000
Number of stock options vested (in shares)	0
Total fair value of stock options vesting (less than $0.1 million in 2014)	$ 0		$ 100,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	10 years
Vesting period in years	4 years