Earnings Per Share - Schedule of Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net Income									$ 96,965	$ 77,130	$ 37,773
Noncontrolling interests									735	(1,940)	(101)
Allocation of earnings to preferred stockholders									0		(64)
Net Income Attributable to Common Stockholders	$ 18,879	$ 37,340	$ 19,543	$ 21,938	$ 24,756	$ 21,089	$ 15,385	$ 13,960	$ 97,700	$ 75,190	$ 37,608
Shares:
Basic: Weighted-average number of shares outstanding									9,091	8,188	7,727
Plus: Incremental shares from assumed conversion of dilutive instruments									201	245	346
Diluted: Weighted-average number of shares outstanding									9,292	8,433	8,073
Earnings per share-Basic	$ 2.09	$ 4.10	$ 2.14	$ 2.41	$ 2.72	$ 2.64	$ 1.97	$ 1.79	$ 10.75	$ 9.18	$ 4.87
Earnings per share-Diluted	$ 2.05	$ 4.02	$ 2.10	$ 2.34	$ 2.65	$ 2.56	$ 1.91	$ 1.73	$ 10.51	$ 8.92	$ 4.66