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 Common Class A [Member]	Dec. 31, 2013 Employee And Directors Stock Options [Member]	Jun. 30, 2014 Employee And Directors Stock Options [Member]	Jun. 30, 2014 Employee And Directors Stock Options [Member] Common Class A [Member]	Jun. 30, 2014 Restricted Stock [Member]	Jun. 30, 2014 Restricted Stock [Member] Common Class A [Member]	Jun. 30, 2014 Time Based Restricted Stock And Stock Option [Member] item	Jun. 30, 2014 Time Based Stock Option [Member] Black Scholes Pricing Model [Member]	Jun. 30, 2013 Time Based Stock Option [Member] Black Scholes Pricing Model [Member]	Jun. 30, 2014 Time Based Stock Option [Member] Minimum [Member] Black Scholes Pricing Model [Member]	Jun. 30, 2014 Time Based Stock Option [Member] Maximum [Member] Black Scholes Pricing Model [Member]	Jun. 30, 2014 Time Based Restricted Stock [Member]	Jun. 30, 2014 Event Based Restricted Stock And Stock Option [Member] Common Class A [Member]	Jun. 30, 2014 Event Based Restricted Stock And Stock Option [Member] Common Class A [Member] Minimum [Member] item	Jun. 30, 2014 Event Based Stock Option [Member]	Jun. 30, 2013 Event Based Stock Option [Member] Monte Carlo Simulation Model [Member]	Jun. 30, 2013 Event Based Stock Option [Member] Minimum [Member] Monte Carlo Simulation Model [Member]	Jun. 30, 2013 Event Based Stock Option [Member] Maximum [Member] Monte Carlo Simulation Model [Member]	Jun. 30, 2014 Event Based Restricted Stock [Member]	Jun. 30, 2013 Event Based Restricted Stock [Member] Monte Carlo Simulation Model [Member]	Jun. 30, 2013 Event Based Restricted Stock [Member] Minimum [Member] Monte Carlo Simulation Model [Member]	Jun. 30, 2013 Event Based Restricted Stock [Member] Maximum [Member] Monte Carlo Simulation Model [Member]
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)																	$ 15.00
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