Calculation of Basic and Diluted Weighted Average Shares Outstanding and Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Basic:
Net income	$ 1,752	[1],[2]	$ 36,102	$ 39,022	$ 40,758	$ 44,246	$ 23,659	$ 30,547	$ 50,974	$ 117,634	$ 149,426	$ 194,332
Net income attributable to participating securities										(2,817)	(2,984)	(3,670)
Net income attributable to common stock-basic										114,817	146,422	190,662
Diluted:
Net income	1,752	[1],[2]	36,102	39,022	40,758	44,246	23,659	30,547	50,974	117,634	149,426	194,332
Net income attributable to participating securities										(2,815)	(2,982)	(3,667)
Net income attributable to common stock-diluted										$ 114,819	$ 146,444	$ 190,665
Weighted average shares (denominator):
Weighted average shares-basic										48,693	48,319	47,988
Dilutive effect of stock options										42	42	42
Weighted average shares-diluted										48,735	48,361	48,030
Basic earnings per share	$ 0.04		$ 0.72	$ 0.78	$ 0.82	$ 0.89	$ 0.48	$ 0.62	$ 1.04	$ 2.36	$ 3.03	$ 3.97
Diluted earnings per share	$ 0.04		$ 0.72	$ 0.78	$ 0.82	$ 0.89	$ 0.48	$ 0.62	$ 1.04	$ 2.36	$ 3.03	$ 3.97

[1] Includes franchise tax settlement of $12,590 before income tax effect ($8,058, net of income tax effect).

[2] Includes loss on early extinguishment of debt of $27,279 before income tax effect ($17,459 net of income tax effect).