Net Income Per Share - Reconciliation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Net Income
Net income available to common stockholders	$ 17,693	$ 16,172
Diluted net income per share	$ 17,693	$ 16,172
Weighted-Average Shares
Net income available to common stockholders (in shares)	40,690,573	37,709,883
Effect of dilutive stock options and warrants (in shares)	226,399	290,191
Diluted net income per share (in shares)	40,916,972	38,000,074
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.43	$ 0.43
Diluted net income per share (in dollars per share)	$ 0.43	$ 0.43