Stockholder's Equity (Details) (USD $) | 3 Months Ended | 6 Months Ended | | 3 Months Ended | 6 Months Ended | | 6 Months Ended | | 6 Months Ended | | 6 Months Ended |
Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Dec. 31, 2013 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2013 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2013 | Jun. 30, 2013 |
Common Class A [Member] | Employee And Directors Stock Options [Member] | Employee And Directors Stock Options [Member] | Employee And Directors Stock Options [Member] | Restricted Stock [Member] | Restricted Stock [Member] | Time Based Restricted Stock And Stock Option [Member] | Time Based Stock Option [Member] | Time Based Stock Option [Member] | Time Based Stock Option [Member] | Time Based Stock Option [Member] | Time Based Restricted Stock [Member] | Event Based Restricted Stock And Stock Option [Member] | Event Based Restricted Stock And Stock Option [Member] | Event Based Stock Option [Member] | Event Based Stock Option [Member] | Event Based Stock Option [Member] | Event Based Stock Option [Member] | Event Based Restricted Stock [Member] | Event Based Restricted Stock [Member] | Event Based Restricted Stock [Member] | Event Based Restricted Stock [Member] |
| | | Common Class A [Member] | | Common Class A [Member] | item | Black Scholes Pricing Model [Member] | Black Scholes Pricing Model [Member] | Minimum [Member] | Maximum [Member] | | Common Class A [Member] | Common Class A [Member] | | Monte Carlo Simulation Model [Member] | Minimum [Member] | Maximum [Member] | | Monte Carlo Simulation Model [Member] | Minimum [Member] | Maximum [Member] |
| | | | | | | | | Black Scholes Pricing Model [Member] | Black Scholes Pricing Model [Member] | | | Minimum [Member] | | | Monte Carlo Simulation Model [Member] | Monte Carlo Simulation Model [Member] | | | Monte Carlo Simulation Model [Member] | Monte Carlo Simulation Model [Member] |
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Equity Incentive Plans | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Shares authorized for issuance | ' | ' | ' | ' | 4,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Granted (in shares) | ' | ' | ' | ' | ' | ' | ' | ' | 79,000 | 1,300,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Shares available for issuance | 1,100,000 | ' | 1,100,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Number of equal annual installments for vesting of awards | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 3 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Closing price per share to be attained for vesting of awards to begin (in dollars per share) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | $15 | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Number of trading days on which the closing price per share should attain the specified price per share for vesting of awards to begin | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 10 | ' | ' | ' | ' | ' | ' | ' | ' |
Stock-Based Compensation | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Stock-based compensation expense (in dollars) | $1,700,000 | $3,100,000 | $3,200,000 | $4,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Unrecognized compensation cost related to non-vested stock options (in dollars) | ' | ' | ' | ' | ' | ' | 4,200,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Unrecognized compensation cost related to non-vested restricted stock (in dollars) | ' | ' | ' | ' | ' | ' | ' | ' | 5,400,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Weighted-average periods over which unrecognized compensation cost recognized | ' | ' | ' | ' | ' | ' | '2 years 7 months 6 days | ' | '1 year 8 months 12 days | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Estimated forfeitures (as a percent) | ' | ' | ' | ' | ' | ' | 1.50% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Number of shares | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the beginning of the period (in shares) | ' | ' | ' | ' | ' | ' | 1,730,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Granted (in shares) | ' | ' | ' | ' | ' | ' | 80,000 | 1,800,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the end of the period (in shares) | ' | ' | ' | ' | ' | 1,730,000 | 1,810,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Vested at the end of the period (in shares) | ' | ' | ' | ' | ' | ' | 608,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Exercisable at the end of the period (in shares) | ' | ' | ' | ' | ' | ' | 608,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Weighted-average exercise price | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the beginning of the period (in dollars per share) | ' | ' | ' | ' | ' | ' | $11.20 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Granted (in dollars per share) | ' | ' | ' | ' | ' | ' | $11.51 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the end of the period (in dollars per share) | ' | ' | ' | ' | ' | $11.20 | $11.21 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Vested at the end of the period (in dollars per share) | ' | ' | ' | ' | ' | ' | $11.05 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Exercisable at the end of the period (in dollars per share) | ' | ' | ' | ' | ' | ' | $11.05 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Weighted-average remaining contractual term | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the beginning of the period | ' | ' | ' | ' | ' | '9 years 3 months 18 days | '8 years 10 months 24 days | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Granted | ' | ' | ' | ' | ' | ' | '9 years 10 months 24 days | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the end of the period | ' | ' | ' | ' | ' | '9 years 3 months 18 days | '8 years 10 months 24 days | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Vested at the end of the period | ' | ' | ' | ' | ' | ' | '8 years 9 months 18 days | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Exercisable at the end of the period | ' | ' | ' | ' | ' | ' | '8 years 9 months 18 days | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Aggregate intrinsic value | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the beginning of the period (in dollars) | ' | ' | ' | ' | ' | ' | 2,208,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the end of the period (in dollars) | ' | ' | ' | ' | ' | 2,208,000 | 3,228,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Vested at the end of the period (in dollars) | ' | ' | ' | ' | ' | ' | 1,180,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Exercisable at the end of the period (in dollars) | ' | ' | ' | ' | ' | ' | $1,180,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Unvested options | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 300,000 | ' | ' | ' | ' | ' | ' | ' |
Number of shares | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the beginning of the period (in shares) | ' | ' | ' | ' | ' | ' | ' | ' | 945,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 200,000 | ' | ' | ' |
Granted (in shares) | ' | ' | ' | ' | ' | ' | ' | ' | 79,000 | 1,300,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Vested (in shares) | ' | ' | ' | ' | ' | ' | ' | ' | -285,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the end of the period (in shares) | ' | ' | ' | ' | ' | ' | ' | ' | 739,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 200,000 | ' | ' | ' |
Weighted-average grant date fair value | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the beginning of the period (in dollars per share) | ' | ' | ' | ' | ' | ' | ' | ' | $10.18 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Granted (in dollars per share) | ' | ' | ' | ' | ' | ' | ' | ' | $11.34 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Vested (in dollars per share) | ' | ' | ' | ' | ' | ' | ' | ' | $11.25 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding at the end of the period (in dollars per share) | ' | ' | ' | ' | ' | ' | ' | ' | $9.89 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Valuation assumptions | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Risk-free interest rate, minimum (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 1.76% | 0.93% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Risk-free interest rate, maximum (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 1.81% | 2.03% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Risk-free interest rates (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 1.78% | ' | ' | ' | 0.52% | ' | ' |
Dividend yield (as a percent) | ' | ' | ' | ' | ' | ' | 0.00% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Volatility, minimum (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 34.40% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Volatility, maximum (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 36.70% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Volatility (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 28.40% | ' | ' | ' | ' | ' | ' | ' | 36.70% | ' | ' | ' | 36.70% | ' | ' |
Weighted-average expected term | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | '6 years | '6 years | '6 years 3 months 18 days | ' | ' | ' | ' | ' | '5 years 4 months 24 days | '5 years 9 months 18 days | ' | ' | '7 months 6 days | '1 year 3 months 18 days |
Vesting period | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | '3 years | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |