Earnings Per Share - Summary of Numerator and Denominator of Basic and Fully Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 7,024	$ 22,022	$ 13,080	$ 47,400
Less: Income attributable to participating securities	(306)	(1,231)	(608)	(2,730)
Basic Earnings Per Share:
Income allocated to common stockholders, Income (Numerator)	$ 6,718	$ 20,791	$ 12,472	$ 44,670
Income allocated to common stockholders, Shares (Denominator)	9,399	9,580	9,489	9,560
Income allocated to common stockholders, Per Share Amount	$ 0.71	$ 2.17	$ 1.31	$ 4.67
Diluted Earnings Per Share:
Income available to common stockholders and assumed conversions, Income (Numerator)	$ 7,736	$ 21,912	$ 12,472	$ 46,901
Income available to common stockholders and assumed conversions, Shares (Denominator)	10,907	11,345	9,551	11,334
Income available to common stockholders and assumed conversions, Per Share Amount	$ 0.71	$ 1.93	$ 1.31	$ 4.14
Convertible Senior Notes [Member]
Effect of Dilutive Securities:
Dilutive Securities, Income (Numerator)	$ 1,018	$ 1,121		$ 2,231
Dilutive Securities, Shares (Denominator)	1,446	1,650		1,649
Stock Options [Member]
Effect of Dilutive Securities:
Dilutive Securities, Income (Numerator)	$ 0	$ 0	$ 0	$ 0
Dilutive Securities, Shares (Denominator)	62	115	62	125