Earnings Per Common Share Basic and Diluted (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator - basic and diluted
Net income (loss)	$ 921	$ 22,522	$ 17,247	$ 18,117	$ (7,139)	$ (50,621)	$ 23,486	$ 23,680	$ 58,807	$ (10,594)	$ (36,986)
Denominator
Weighted average number of common shares outstanding - basic	39,991,000	39,789,000	39,681,000	39,438,000	39,115,000	39,094,000	39,143,000	39,403,000	39,726,000	39,188,000	40,316,000
Effect of dilutive stock options									375,000
Effect of dilutive restricted shares									628,000
Weighted average number of common shares outstanding - diluted	41,090,000	40,819,000	40,750,000	40,457,000	39,115,000	39,094,000	40,293,000	40,620,000	40,729,000	39,188,000	40,316,000
Earnings (loss) per common share - basic	$ 0.02	$ 0.57	$ 0.43	$ 0.46	$ (0.18)	$ (1.29)	$ 0.60	$ 0.60	$ 1.48	$ (0.27)	$ (0.92)
Earnings (loss) per common share - diluted	$ 0.02	$ 0.55	$ 0.42	$ 0.45	$ (0.18)	$ (1.29)	$ 0.58	$ 0.58	$ 1.44	$ (0.27)	$ (0.92)
Stock Options and Restricted Shares
Denominator
Anti-dilutive securities excluded from computation of earnings per share									2,967,000	4,363,000	4,943,000