Stockholders' Equity (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Stockholders' Equity
Equity compensation expense	$ 1,960,000	$ 1,260,000
Fair value weighted-average assumptions:
Expected life of options	5 months 27 days
Aggregate Intrinsic Value
Unrecognized compensation cost related to unvested restricted stock awards (in dollars)	700,000
Nonqualified Cash Plan
Stockholders' Equity
Deferred compensation liability, noncurrent	400,000		100,000
Trading securities	400,000
Common stock options
Stockholders' Equity
Total unrecognized compensation cost related to non-vested stock options granted (in dollars)	13,400,000
Period of recognition compensation cost	3 years
Fair value weighted-average assumptions:
Expected stock price volatility (as a percent)	77.10%	81.40%
Risk free interest rate (as a percent)	1.70%	2.00%
Expected life of options	6 years 3 months	6 years 3 months
Expected annual dividend per share (in dollars per share)	$ 0.00	$ 0.00
Number of Shares
Balance at the beginning of the period (in shares)	10,020,700
Options granted (in shares)	1,415,700
Options exercised (in shares)	(818,700)
Options forfeited (in shares)	(15,000)
Balance at the end of the period (in shares)	10,602,700
Vested and unvested expected to vest at the end of the period (in shares)	9,842,500
Exercisable at the end of the period (in shares)	5,261,000
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 5.02
Options granted (in dollars per share)	$ 9.07
Options exercised (in dollars per share)	$ 5.02
Options forfeited (in dollars per share)	$ 2.80
Balance at the end of the period (in dollars per share)	$ 5.56
Vested and unvested expected to vest at the end of the period (in dollars per share)	$ 5.58
Exercisable at the end of the period (in dollars per share)	$ 6.30
Weighted Average Remaining Contractual Life
Balance at the end of the period	7 years 3 months 18 days
Vested and unvested expected to vest at the end of the period	7 years 2 months 12 days
Exercisable at the end of the period	5 years 8 months 12 days
Aggregate Intrinsic Value
Aggregate intrinsic value of options outstanding (in dollars)	57,600
Aggregate intrinsic value of options vested and unvested expected to vest (in dollars)	53,400
Aggregate intrinsic value of options exercisable (in dollars)	25,300
Restricted stock units (RSUs)
Stockholders' Equity
Period of recognition compensation cost	5 months 27 days
Number of Shares
Balance at the beginning of the period (in shares)	955,000
Balance at the end of the period (in shares)	955,000
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 2.28
Balance at the end of the period (in dollars per share)	$ 2.28
Aggregate Intrinsic Value
Aggregate intrinsic value, nonvested (in dollars)	8,200,000
Options vested	0
Maximum | Nonqualified Cash Plan
Stockholders' Equity
Income from investments	1,000
Unrealized gain/loss	$ 1,000