Schedule of Reconciliation of Numerator and Denominator of Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Earnings Per Share [Abstract]
Net income (loss)	$ 19,091		$ 14,803		$ 55,070		$ (44,660)
Weighted average common shares outstanding	78,666,241		81,905,566		78,485,109		77,890,406
Weighted average potential dilutive common shares	550,683	[1],[2]	956,972	[1],[2]	708,343	[1],[2]
Weighted average common shares outstanding - assuming dilution	79,216,924		82,862,538		79,193,452		77,890,406
Net income (loss) per common share - basic	$ 0.24		$ 0.18		$ 0.70		$ (0.57)
Net income (loss) per common share - diluted	$ 0.24		$ 0.18		$ 0.70		$ (0.57)

[1] Potential common shares consist of common stock issuable under the assumed exercise of stock options and restricted stock awards using the treasury stock method.

[2] For the nine months ended September 30, 2013, 2,784,779 potential common shares consisting of common stock under the assumed exercise of stock options and restricted stock awards using the treasury stock method were not included in the computation of the diluted net income (loss) per share since their inclusion would have an antidilutive effect.