Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net income available to common shareholders	$ 13,224	$ 8,339	$ 34,793	$ 20,651
Denominator:
Basic weighted average shares outstanding	17,012,046	15,571,207	16,947,935	15,522,492
Effect of dilutive securities:
SARs and options	286,869	445,178	308,472	447,932
Convertible notes		1,155,920		965,967
Restricted stock	93,355	37,872	80,307	27,691
Diluted weighted average shares outstanding	17,392,270	17,210,177	17,336,714	16,964,082
Basic earnings per share	$ 0.78	$ 0.54	$ 2.05	$ 1.33
Diluted earnings per share	$ 0.76	$ 0.48	$ 2.01	$ 1.22