Common Stock (Stock Option Activity and Additional Details) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	0	0	0
Shares
Outstanding, beginning of period	1,544,960
Exercised	(767,560)	(311,954)
Forfeited	0
Expired	0
Outstanding, end of period	777,400	1,544,960
Vested or expected to vest	777,400
Options exercisable	777,400
Weighted-Average Exercise Price (in dollars per share)
Outstanding, beginning of period (in dollars per share)	$ 4.81
Exercised (in dollars per share)	1.79
Forfeited (in dollars per share)	0.00
Expired (in dollars per share)	0.00
Outstanding, end of period (in dollars per share)	7.80	$ 4.81
Vested or expected to vest (in dollars per share)	7.80
Options exercisable (in dollars per share)	$ 7.80
Weighted Average Remaining Conctracual Term (in years)
Outstanding	1 year 3 months 22 days
Vesting or expected to vest	1 year 3 months 22 days
Options exercisable	1 year 3 months 22 days
Aggregate Intrinsic Value
Outstanding	$ 2,828,951
Vesting or expected to vest	2,828,951
Options exercisable	2,828,951
Stock Options, Additional Disclosures
Total intrinsic value of stock options exercised	$ 8,400,000	$ 6,000,000	$ 5,600,000
Number of stock options vested	0
Total fair value of stock options vesting (less than $0.1 million in 2014)		$ 100,000	$ 4,200,000
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	10 years
Vesting period in years	4 years