Earnings Per Share - Components of Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income (loss) available to common shareholders	$ 20,048	$ 20,107	$ 40,575	$ 42,240
Weighted-average number of common shares outstanding - basic (shares)	31,564,893	30,641,554	31,495,082	30,524,955
Share-based compensation plans (shares)	807,258	1,910,634	823,245	2,129,773
Warrants (shares)	8,511	17,464	8,566	27,318
Weighted-average number of common shares - diluted (shares)	32,380,662	32,569,652	32,326,893	32,682,046
Basic earnings per common share (usd per share)	$ 0.64	$ 0.66	$ 1.29	$ 1.38
Diluted earnings per common share (usd per share)	$ 0.62	$ 0.62	$ 1.26	$ 1.29