Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Calculation of Basic Earnings Per Share:
Net Income	$ 5,134	$ 4,356	$ 22,815	$ 19,225	$ 32,787
Weighted shares outstanding - Basic (in shares)	9,704,161	9,621,580	9,681,422	9,611,610
Basic Earnings Per Share (in usd per share)	$ 0.53	$ 0.45	$ 2.36	$ 2.00
Reconciliation of Numerator:
Net Income	5,134	4,356	22,815	19,225	32,787
Effect of 8.25% Convertible debentures	0	11	0	22
Adjusted numerator-Diluted	$ 5,134	$ 4,367	$ 22,815	$ 19,247
Reconciliation of Denominator:
Weighted shares outstanding - Basic (in shares)	9,704,161	9,621,580	9,681,422	9,611,610
Effect of dilutive securities:
Share-based Compensation (in shares)	33,691	22,454	34,340	22,789
8.25% Convertible debentures (in shares)	0	51,436	0	52,854
Adjusted denominator-Diluted (in shares)	9,737,852	9,695,470	9,715,762	9,687,253
Diluted Earnings Per Share (in usd per share)	$ 0.53	$ 0.45	$ 2.35	$ 1.99