Summary of Significant Accounting Policies - Additional Information 2 (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) Unit $ / shares $ / EquityUnit shares	Sep. 30, 2014 USD ($) shares	Sep. 30, 2015 USD ($) Unit $ / shares $ / EquityUnit shares	Sep. 30, 2014 USD ($) shares	Dec. 31, 2014 shares
Operations And Summary Of Significant Accounting Policies [Line Items]
Stock-based compensation expense recognized			$ 6,061,000	$ 7,842,000
Federal
Operations And Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets valuation allowance	$ 178,600,000		178,600,000
State
Operations And Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets valuation allowance	$ 71,600,000		$ 71,600,000
Restricted Stock
Operations And Summary Of Significant Accounting Policies [Line Items]
Number of shares granted | shares			1,010,371
Restricted stock grant date fair value			$ 5,400,000
Grant date fair value of share units, per unit | $ / shares			$ 5.34
Shares of unvested restricted stock outstanding | shares	1,575,302		1,575,302		1,207,527
Weighted average grant date fair value of stock grants per share | $ / shares	$ 9.90		$ 9.90
Unrecognized compensation cost	$ 6,600,000		$ 6,600,000
Period in which compensation cost expected to be recognized			1 year 6 months
Potential Performance Shares
Operations And Summary Of Significant Accounting Policies [Line Items]
Unrecognized compensation cost	$ 2,600,000		$ 2,600,000
Period in which compensation cost expected to be recognized			1 year 10 months 24 days
Number of units granted | Unit			471,249
Performance units grant date fair value			$ 2,100,000
Grant date fair value of share units, per unit | $ / EquityUnit			4.38
Number of performance stock units ("PSUs") outstanding | Unit	669,604		669,604
Weighted average grant date fair value of PSUs per unit | $ / EquityUnit	9.13		9.13
Potential Performance Shares | Minimum
Operations And Summary Of Significant Accounting Policies [Line Items]
Common stock, shares, potentially issuable in exchange for Share Units | shares	0		0
Potential Performance Shares | Maximum
Operations And Summary Of Significant Accounting Policies [Line Items]
Common stock, shares, potentially issuable in exchange for Share Units | shares	1,400,173		1,400,173
Stock Options
Operations And Summary Of Significant Accounting Policies [Line Items]
Unrecognized compensation cost	$ 0		$ 0
Number of Options Outstanding | shares	102,650		102,650
Weighted average exercise price | $ / shares	$ 32.94		$ 32.94
Number of option, Exercised | shares	0	0	0	0
General and Administrative Expense
Operations And Summary Of Significant Accounting Policies [Line Items]
Stock-based compensation expense recognized	$ 2,100,000	$ 2,800,000	$ 6,100,000	$ 7,800,000