Earnings Per Share - Computation of Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income attributable to common shareholders	$ 28,532	$ 20,576	$ 50,983	$ 37,249	$ 88,531	$ 74,126	$ 55,128
Denominator:
Denominator for basic earnings per share - weighted average shares	35,377,694	32,799,837	34,853,731	32,591,917
Effect of Dilutive Securities:
Stock options and non-vested stock	225,000	180,000	225,000	167,000
Denominator for diluted earnings per share - adjusted weighted average shares and assumed conversion	35,603,020	32,979,708	35,078,946	32,759,069
Basic earnings per common share attributable to common shareholders	$ 0.81	$ 0.63	$ 1.46	$ 1.14	$ 2.68	$ 2.37	$ 1.88
Diluted earnings per common share attributable to common shareholders	$ 0.80	$ 0.62	$ 1.45	$ 1.14	$ 2.67	$ 2.36	$ 1.87