Components of Income Tax Expense (Benefit) from Continuing Operations (Detail) - USD ($) $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax
Federal											$ (8,260)	$ 41,860	$ 29,622
State											1,889	1,570	2,753
Total current tax (benefit) expense											(6,371)	43,430	32,375
Deferred tax
Federal											57,851	1,145	301
State											1,890	380	(946)
Total deferred tax expense (benefit)											59,741	1,525	(645)
Total tax expense	$ 16,463	$ 12,971	$ 11,490	$ 12,446	$ 10,939	$ 10,674	$ 12,102		$ 11,240		$ 53,370	$ 44,955	$ 31,730

[1] During the third quarter of 2016, the Company early adopted ASU No. 2016-09 with an effective date of January 1, 2016. As part of the adoption of this standard, the Company made an accounting policy election to account for stock compensation forfeitures on an actual basis and discontinue the use of an estimated forfeiture approach. This change required a modified retrospective adoption, via a cumulative effect adjustment and recasting of first quarter and second quarter 2016 operating results. The impact of this adoption was an increase to net income of $158 thousand and $220 thousand for the first and second quarters, respectively. Additionally, basic and diluted net income per share increased $0.01 for both periods.