Employee Benefits - Components of Salaries and Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Salaries and benefits									$ 181,416	$ 154,638	$ 83,563
Annual incentive compensation									32,030	36,482	32,107
Share-based compensation expense									14,882	10,885	2,923
Pension plans									10,260	9,217	6,023
Total salaries and benefits	$ 72,685	$ 55,440	$ 52,691	$ 57,772	$ 69,624	$ 54,525	$ 55,683	$ 31,390	$ 238,588	$ 211,222	$ 124,616